Monday, November 11, 2019

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2797

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2797

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2796

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2796

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

programming

U0134

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2795

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2795

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2794

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2794

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2793

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2793

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

programming

U0132

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2792

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2792

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2791

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2791

U0131

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2790

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2790

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2789

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2789

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2788

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2788

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

programming

U0129

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2787

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2787

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

2019 Cadillac Truck Escalade AWD V8-6.2L Diagnostic Instructions Page 14


B0012 02 Stage 1 or B0013 02 Stage 2



The driver steering wheel air bag high and/or low circuit is shorted to ground for 120 milliseconds.



B0012 04 Stage 1 or B0013 04 Stage 2



The driver steering wheel air bag high and/or low circuit is open for 120 milliseconds.



B0012 0D Stage 1 or B0013 0D Stage 2



The driver steering wheel air bag deployment loop resistance is greater than 5.1 ohms for 120 milliseconds.



B0012 0E Stage 1 or B0013 0E Stage 2



The driver steering wheel air bag deployment loop resistance is less than 1.3 ohms for 120 milliseconds.



Action Taken When the DTC Sets



* The SDM requests the instrument panel cluster (IPC) to illuminate the AIR BAG indicator.



* The SDM will store a DTC, however if an event occurs the system will still attempt deployments.



Conditions for Clearing the DTC



* The condition for setting the DTC no longer exists.



* A history DTC will clear once 100 malfunction-free ignition cycles have occurred.



Diagnostic Aids



* When a harness connector is disconnected, the high control and low control circuits are shorted together by the integral shorting bar. This



should be taken into account when testing for faults on these circuits.



* This DTC usually indicates a poor connection or a wiring malfunction between the SDM and the deployment loop.



Reference Information



Schematic Reference



SIR Schematics (See: Diagrams/Electrical Diagrams/Air Bag Systems)



Connector End View Reference



Component Connector End Views (See: Diagrams/Connector Views)



Description and Operation



SIR System Description and Operation (See: Restraints and Safety Systems/Air Bag Systems/Description and Operation)



Electrical Information Reference



* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit



Testing/Circuit Testing)



* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic



Procedures/Connector Repairs/Connector Repairs)



* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General



Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)



* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring



Repairs/Wiring Repairs)



Scan Tool Reference



Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information



Special Tools



J 38715-A SIR Driver/Passenger Load Tool



Circuit/System Testing



Important: When removing connectors inspect for damage, corrosion or poor connection. Damage or corrosion to the following requires



repair or replacement of the affected component/connector:



* Driver steering wheel air bag

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2786

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2786

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2785

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2785

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

programming

U0128

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2784

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2784

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2783

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2783

U0126

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2782

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2782

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2781

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2781

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2780

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2780

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

programming

U0123

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

2010 Cadillac Truck SRX AWD V6-2.8L Turbo Page 1274

2010 Cadillac Truck SRX AWD V6-2.8L Turbo Page 1274



knock sensor system determines that excessive knock is present, the engine control module (ECM) retards the spark timing based on the signal



from the knock sensor system. The knock sensor produces an AC signal when specific frequencies are detected. The ECM then retards the timing



until knock is controlled.



In order to differentiate between normal engine noise and spark knock, the ECM samples the knock sensor signal. The ECM samples the knock



sensor signal for a certain length of time under different engine speeds and loads during non-cylinder knock events. This sampling is used to



determine a range of acceptable normal engine noise.



Conditions for Running the DTC



P0326 and P0331



* The engine speed is greater than 1,600 RPM.



* The ECM is controlling spark.



* DTCs P0326 and P0331 run continuously once the above conditions are met.



P0327, P0328, P0332, and P0333



* DTCs P0324, P0335, P0336, P0338, P0341, P0342, P0343, P0346, P0347, P0348, P0366, P0367, P0368, P0391, P0392, P0393 are not set.



* The engine speed is greater than 1,960 RPM.



* The ECM is controlling spark.



* The increase in engine speed is less than a range of 1,400-3,700 RPM per second.



* The engine load is in the range of 35-65 kPa per second.



* DTCs P0327, P0328, P0332, and P0332 run continuously once the above conditions are met for approximately 20 s.



Conditions for Setting the DTC



P0326 and P0331



The ECM detects a knock sensor signal voltage that is not in the range of a predetermined engine noise level in 25 of 250 test samples. The



condition exists for greater than 1 s or for a cumulative of 10 s.



P0327 or P0332



The ECM detects a knock sensor signal voltage that is less than the predetermined minimum engine noise level for greater than 1 s or for a



cumulative of 10 s.



P0328 or P0333



The ECM detects the knock sensor signal voltage is greater than predetermined maximum engine noise level for greater than 1 s or for a cumulative



of 10 s.



Action Taken When the DTC Sets



DTCs P0326, P0327, P0328, P0331, P0332, and P0333 are Type B DTCs.



Conditions for Clearing the DTC



DTCs P0326, P0327, P0328, P0331, P0332, and P0333 are Type B DTCs.



Diagnostic Aids



* Inspect the knock sensor for physical damage. A knock sensor that is dropped or damaged may cause a DTC to set.



* Inspect the knock sensor for proper installation. A knock sensor that is loose or over torqued may cause a DTC to set. The knock sensor



should be free of thread sealant. The knock sensor mounting surface should be free of burrs, casting flash, and foreign material.



* The knock sensor must be clear of hoses, brackets, and engine electrical wiring.



* With the knock sensor disconnected, the normal voltage measured from the knock sensor signal or the low reference circuit to ground is



between 2.30-2.80 V.



Reference Information



Schematic Reference



Engine Controls Schematics (LAU) (See: Diagrams/Electrical Diagrams/Powertrain Management/System Diagram)Engine Controls Schematics



(LF1) (See: Diagrams/Electrical Diagrams/Powertrain Management/System Diagram)



Connector End View Reference



Component Connector End Views (See: Diagrams/Connector Views/Connector End Views By Name)



Description and Operation



Knock Sensor System Description (See: Powertrain Management/Computers and Control Systems/Knock Sensor/Description and Operation)



Electrical Information Reference

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2779

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2779

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2778

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2778

Circuit/System Description

The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the

serial data circuit through the DLC, the scan tool can be used to monitor each control module for diagnostic purposes and to check for diagnostic

trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health

(SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for

example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on

the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn set a DTC associated with the

loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating and one or more

control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that

contain the stored code.

Conditions for Running the DTC

The system voltage is between 9-16 V.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

* Specific subsystems will not function.

* DTC U0100 in the TCM will cause the transmission to go into default gears.

* Both DTC U0100 in the TCM and DTC U0101 in the ECM will cause the malfunction indicator lamp (MIL) to illuminate.

Conditions for Clearing the DTC

* The ECM/TCM turns OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.

* A current DTC clears when the malfunction is no longer present.

* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Diagnostic Aids

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2777

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2777

* The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Determine the control module that is not communicating. Refer to Control Module U Code List (See: Diagnostic Trouble Code

Descriptions/Control Module U Code List).

2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.

3. Test for less than 10 ohm between each ground circuit terminal and ground.

瀚慖f greater than the specified range, test the ground circuit for an open/high resistance.

4. If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the

control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test

the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.

Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit,

and the BCM is the output for these circuits. Refer to the control module schematics to identify which control modules have these circuits.

6. If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup

circuit terminal and ground.

瀚慖f the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

7. Ignition OFF for 60 seconds, test for less than 5 ohm between the serial data circuit terminals and the appropriate DLC terminal listed below:

* Class 2 serial data circuit terminal 2

* Low speed GMLAN serial data terminal 1

* High speed GMLAN serial data terminal 6 or 14

瀚慖f greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module

and a control module setting the DTC or a serial data splice pack.

8. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Wiring Repairs/GMLAN Wiring Repairs)

* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and

programming

U0122

DTC U0100-U02FF (without HP2)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System

Check - Vehicle) prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an

overview of the diagnostic approach.

* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure

Instructions) provides an overview of each diagnostic category.

DTC Descriptor

Refer to Control Module U Code List (See: Diagnostic Trouble Code Descriptions/Control Module U Code List).

Diagnostic Fault Information

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2776

2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2776

* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no

associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are

transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically

after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:

- A control module on the data communication circuit was disconnected while the communication circuit is awake.

- Power to one or more control modules was interrupted during diagnosis.

- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.

- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.

- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above.

These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between

control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a

control module based only on a history U-code.

* Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication

issue.

* Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system

inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.

* Use Data Link References (See: Powertrain Management/Computers and Control Systems/Information Bus/Testing and Inspection/Initial

Inspection and Diagnostic Overview) to determine if the control module uses high or low speed GMLAN serial data communications.

* Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and

the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control

module.

* This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to,

providing the vehicle is equipped with the control module.

Reference Information

Schematic Reference

* Data Communication Schematics (See: Powertrain Management/Computers and Control Systems/Information Bus/Diagrams/Electrical

Diagrams)

* Control Module References (See: Testing and Inspection/Programming and Relearning)

Connector End View Reference

Component Connector End Views (See: Diagrams/Connector Views)

Description and Operation

Data Link Communications Description and Operation (See: Powertrain Management/Computers and Control Systems/Information

Bus/Description and Operation)

Electrical Information Reference

* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit

Testing/Circuit Testing)

* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic

Procedures/Connector Repairs/Connector Repairs)

* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General

Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)

* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring

Repairs/Wiring Repairs)

Scan Tool Reference

Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information

Circuit/System Verification

Verify that DTC U1814, U2099, B1428, B1370, B1380, B1440, or B1441 is not set.

If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions/Diagnostic

Trouble Code (DTC) List - Vehicle).

Circuit/System Testing

Note: Use the schematic to identify the following:

* Control modules the vehicle is equipped with

* Control module locations on the low and high speed GMLAN serial data circuits