B127D
DTC B1277, B127C, or B127D
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provide an overview of each diagnostic category.
DTC Descriptors
DTC B1277 01
- Microphone 1 (LF) Input Signal Circuit Short to Battery
DTC B1277 02
- Microphone 1 (LF) Input Signal Circuit Short to Ground
DTC B1277 04
- Microphone 1 (LF) Input Signal Circuit Open
DTC B1277 1A
- Microphone 1 (LF) Input Signal Circuit Bias Level Out of Range
DTC B127C 01
- Microphone 2 (RF) Input Signal Circuit Short to Battery
DTC B127C 02
- Microphone 2 (RF) Input Signal Circuit Short to Ground
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
Diagnostic Fault Information
Circuit/System 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 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 ground 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 Active Noise Cancellation Schematics
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
Description and Operation
Active Noise Cancellation Description and Operation Active Noise Cancellation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the appropriate B77 Interior Noise Microphone. Ignition ON radio ON.
2. Test for 7.8-8.8 V between the microphone high 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.
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 ohms in the signal circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the T3 Audio Amplifier.
• If greater than 8.8 V
1. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier. 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.
• If between 7.8-8.8 V
3. Test for less than 1 V between the microphone low signal circuit terminal 1 and ground.
• If greater than 1 V
1. Ignition OFF, X3 harness connector at the T3 Audio Amplifier. 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.
• If less than 1 V
4. Test for 7.8-8.8 V between the microphone high signal circuit terminal 2 and the low signal circuit terminal 1.
• If not between 7.8-8.8 V
1. Ignition OFF, disconnect the X3 harness connector at the T3 Audio Amplifier.
2. Test for infinite resistance between the microphone low 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 ohms in the microphone low signal circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the T3 Audio Amplifier.
• If between 9.5-10.5 V
5. Test or replace the B77 Interior Noise Microphone.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Radio Volume Compensator Interior Noise Microphone Replacement Service and Repair
* Control Module References Control Module References for amplifier replacement, setup, and programming.