B127C GMC – Microphone 2 Input Signal Circuit

B127C GMC Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

B127C GMC Possible Causes

Faulty Radio Volume Compensator Interior Noise Microphone,Radio Volume Compensator Interior Noise Microphone harness is open or shorted,Radio Volume Compensator Interior Noise Microphone circuit poor electrical connection,Faulty Audio Amplifier

B127C GMC Description

The active noise cancellation system uses three microphones in the vehicle headliner: one above each front seating position, and one above the rear seat. The Audio 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 Audio Amplifier uses the microphone inputs and an engine RPM signal to determine the frequency of the undesirable sound. The Audio Amplifier performs a self diagnostic of the microphone circuits 16 seconds after initial power up, then periodically every 400 milliseconds thereafter.