• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provide an overview of each diagnostic category.

For symptom byte information refer to Symptom Byte List

The active noise cancellation system uses four microphones in the vehicle headliner: one above each front seating position, and two above the rear seats. The Audio Amplifier/Active Noise Cancellation Module 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/Active Noise Cancellation Module performs a self diagnostic of the microphone circuits 16 seconds after initial power up, then periodically every 400 milliseconds thereafter.

• DTC B1325 is not current
• A short to voltage is detected on the specified (+) or (−) signal circuit for more than 1.5 seconds

• DTC B1325 is not current
• A short to ground is detected on the specified (+) or (−) signal circuit for more than 1.5 seconds

• DTC B1325 is not current
• An open is detected on the specified (+) or (−) signal circuit for more than 1.5 seconds

• DTC B1325 is not current
• An out of range voltage is detected on the specified (+) or (−) signal circuit for more than 1.5 seconds

The active noise cancellation system is disabled.

• 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.

• 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.

Radio/Navigation System Schematics

Master Electrical Component List

Active Noise Cancellation Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

1. Ignition OFF, disconnect the harness connector at the appropriate B77 Radio Volume Compensator Interior Noise Microphone. Ignition ON.
2. Test for 7.8–8.8 V between the signal circuit terminal 2 and ground.
• If less than 7.8 V
1. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier/K108 Active Noise Cancellation Module.
2. Test for infinite resistance between the signal circuit and ground.
• If less than infinite resistance, repair the short to ground in the circuit.
• If infinite resistance
3. Test for less than 2 Ω in the signal circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, replace the T3 Audio Amplifier/K108 Active Noise Cancellation Module.
• If greater than 8.8 V
1. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier/K108 Active Noise Cancellation Module. Ignition ON.
2. Test for less than 1 V between the signal circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the T3 Audio Amplifier/K108 Active Noise Cancellation Module.
• If between 7.8–8.8 V
3. Test for less than 1 V between the signal circuit terminal 1 and ground.
• If greater than 1 V
1. Ignition OFF, X3 harness connector at the T3 Audio Amplifier/K108 Active Noise Cancellation Module. Ignition ON.
2. Test for less than 1 V between the signal circuit and ground.
• If 1 V or greater, repair the short to voltage in the circuit.
• If less than 1 V, replace the T3 Audio Amplifier/K108 Active Noise Cancellation Module.
• If less than 1 V
4. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier/K108 Active Noise Cancellation Module.
5. Test for infinite resistance between the B77 Radio Volume Compensator Interior Noise Microphone signal circuit terminal 1 and ground.
• If less than infinite resistance

  Repair the short to ground in the circuit

• If infinite resistance
6. Test for less than 2 Ω in the signal circuit end to end.
• If 2 Ω or greater

  Repair the open/high resistance in the circuit

• If less than 2 Ω
7. Replace the B77 Radio Volume Compensator Interior Noise Microphone.
8. Ignition ON
9. Verify the DTC does NOT set.
• If the DTC sets

  Replace the T3 Audio Amplifier/K108 Active Noise Cancellation Module.

• If the DTC does not set
10. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

• Active Noise Cancellation Microphone Replacement
• Control Module References for Audio Amplifier replacement, programming, and setup.