Thursday, July 4, 2019

2019 Cadillac Truck Escalade AWD V8-6.2L Diagnostic Instructions Page 360


DTC B127C 04



- Microphone 2 (RF) Input Signal Circuit Open



DTC B127C 1A



- Microphone 2 (RF) Input Signal Circuit Bias Level Out of Range



DTC B127D 01



- Microphone 3 (RR) Input Signal Circuit Short to Battery



DTC B127D 02



- Microphone 3 (RR) Input Signal Circuit Short to Ground



DTC B127D 04



- Microphone 3 (RR) Input Signal Circuit Open



DTC B127D 1A



- Microphone 3 (RR) Input Signal Circuit Bias Level Out of Range



Circuit/System Description



The active noise cancellation system uses three microphones in the vehicle headliner: one above each front seating position, and another above the



right side of the second row seat. The amplifier provides a bias voltage to each microphone (+) and (-) signal circuits for operation of the



microphone. The microphones monitor the vehicle cabin for undesirable engine sounds. The amplifier uses the microphone inputs and an engine



RPM signal to determine the frequency of the undesirable sound.



Conditions for Running the DTC



The amplifier performs a self diagnostic of the microphone circuits 16 seconds after initial power up, then periodically every 400 milliseconds



thereafter.



Conditions for Setting the DTC



DTC B1277 01, B127C 01, B127D 01



* DTC B1325 is not current



* A short to voltage is detected on the specified (+) or (-) signal circuit for more than 1.5 seconds



DTC B1277 02, B127C 02, B127D 02



* DTC B1325 is not current



* A short to voltage is detected on the specified (+) or (-) signal circuit for more than 1.5 seconds



DTC B1277 04, B127C 04, B127D 04



* DTC B1325 is not current



* An open is detected on the specified (+) or (-) signal circuit for more than 1.5 seconds



DTC B1277 1A, B127C 1A, B127D 1A



* DTC B1325 is not current



* An out of range voltage is detected on the specified (+) or (-) signal circuit for more than 1.5 seconds



Action Taken When the DTC Sets



The active noise cancellation system is disabled.



Conditions for Clearing the DTC



* A current DTC clears when the self diagnostic passes on the next ignition cycle.



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



Diagnostic Aids



* Installation of aftermarket replacement speakers, additional speakers/subwoofers, or aftermarket exhaust systems can cause undesirable



behavior of the active noise cancellation system.



* The noise reduction microphones have foam blocks above them to seal the microphones and aid in the reduction of headliner vibration.



Missing or out of place foam blocks can impact system performance.



Reference Information



Schematic Reference



Active Noise Cancellation Schematics (See: Accessories and Optional Equipment/Diagrams/Electrical Diagrams/Active Noise Cancellation

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