C129D
DTC C0277, C120C, C129A, C129B, C129D, C129E, C12B1, or C12F8
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) provides an overview of each diagnostic category.
DTC Descriptors
DTC C0277 03
- BMC Primary Piston Position Sensor A and B Circuit Performance Voltage Below Threshold
DTC C129A
- Brake Pedal Position Sensor 3 Circuit Low
DTC C129D
- Brake Pedal Position Sensor 4 Circuit Low
DTC C0277 07
- BMC Primary Piston Position Sensor A and B Circuit Voltage Above Threshold
DTC C129B
- Brake Pedal Position Sensor 3 Circuit High
DTC C129E
- Brake Pedal Position Sensor 4 Circuit High
DTC C0277 5A
- BMC Primary Piston Position Sensor A and B Circuit Plausibility Failure
DTC C12B1
- ABS Master Cylinder Pressure Sensor and Brake Pedal Position Sensor Not Plausible
DTC C12F8
- Brake Pedal Position Sensor 3 Not Plausible
DTC C120C
- Brake Pedal Position Sensor 4 Not Plausible
Diagnostic Fault Information
Circuit/System Description
The electronic brake control module (EBCM) uses input from the brake master cylinder piston position sensor and the brake switch to determine when the brake pedal is being applied and with how much force. These inputs are used to determine the driver's braking intent which is used to the control amount of pressure applied to the wheels.
Conditions for Running the DTC
* Ignition ON.
* Ignition voltage is greater than 10 V.
Conditions for Setting the DTC
C0277 03, C129A, or C129D
The EBCM detects voltage below threshold on signal circuit.
C0277 07, C129B, or C129E
The EBCM detects voltage above threshold on signal circuit.
C0277 5A, C12B1, C12F8, or C120C
This EBCM detects the master cylinder pressure is high when brake master cylinder piston position sensor is reading low travel.
Action Taken When the DTC Sets
* The EBCM disables the antilock brake system (ABS), traction control and the vehicle stability enhancement system for the duration of the ignition cycle.
* A driver information center message and/or a warning indicator may be displayed.
Conditions for Clearing the DTC
* The condition for the DTC is no longer present.
* The EBCM clears the history DTC when a current DTC is not detected in 40 consecutive drive cycles.
Reference Information
Schematic Reference
Antilock Brake System Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
ABS Description and Operation (ABS Hybrid (HP2))
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 (Programming and Relearning) for scan tool information
Circuit/System Verification
Note: The battery must be able to maintain a charge during this procedure. It is recommended that a charger/maintainer or equivalent be used to maintain proper battery voltage during this procedure.
1. Ignition ON, engine OFF, using a scan tool access the EBCM, Module Setup screen, and perform the EBCM Relearn. The relearn procedure will verify valve and pressure sensor calibrations are correct.
Note: To ensure the complete brake modulator and high pressure accumulator pressure relief procedure is allowed to occur; the brake controller must see one brake pedal apply with the engine running followed by a proper shutdown without applying the brake pedal.
2. Transmission in PARK, engine running, apply and release the brake pedal.
Note: The ignition must transition to the OFF position without pausing at ACCESSORY and without applying the brake pedal. This ensures that the brake modulator and the high pressure accumulator pressure relief occurs. This process will take approximately 1-2 minutes.
3. Ignition OFF, key removed from the ignition, wait 2 minutes.
Note: The ignition must remain in the ON position with the engine OFF during the following steps.
4. Ignition ON, brake pedal released, verify the following EBCM scan tool parameters are within the specified range:
* BMC Prim. Piston Pos. Sen. 5 V Reference Position - Between 4.75-5.25 V
* BMC Primary Piston Position Sensor A - Between 0.4-0.8 V
* BMC Primary Piston Position Sensor B - Between 4.2-4.6 V
• If any of the parameters are not within the specified range, refer to Circuit/System Testing.
5. Brakes not applied, verify the following EBCM scan tool parameters are within the specified range:
* Master Cylinder Pressure Sensor Input - Less than 100 kPa (15 psi)
* Rear Brake Pressure Sensor - Less than 100 kPa (15 psi)
* Brake Pressure Sensor Input - Less than 100 kPa (15 psi)
* Accum. Pressure Sensor - Less than 800 kPa (116 psi)
• If any of the parameters are not within the specified range, replace the brake pressure modulator valve.
Circuit/System Testing
1. Perform a hydraulic check, refer to Brake Hydraulic and Assist System Diagnosis (Two-mode Hybrid) Brake Pedal Travel Measurement and Inspection
2. Ignition OFF, disconnect the harness connector at the brake master cylinder piston position sensor.
3. Wait 60 seconds, test for less than 5 ohm between the low reference circuit terminal 4 and ground.
• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the EBCM.
4. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal 2 and ground.
• If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.
• If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the EBCM.
5. Verify the scan tool BMC Primary Piston Position Sensor A parameter is less than 1 V.
• If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit tests normal, replace the EBCM.
6. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the 5 V reference circuit terminal 2. Verify the scan tool BMC Primary Piston Position Sensor A parameter is greater than 4.5 V.
• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.
7. Verify the scan tool BMC Primary Piston Position Sensor B parameter is less than 1 V.
• If greater than the specified range, test the signal circuit terminal 1 for a short to voltage. If the circuit tests normal, replace the EBCM.
8. Install a 3 A fused jumper wire between the signal circuit terminal 1 and the 5 V reference circuit terminal 2. Verify the scan tool BMC Primary Piston Position Sensor B parameter is greater than 4.5 V.
• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.
9. If all circuits test normal, replace the brake master cylinder piston position sensor.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Brake Master Cylinder Primary Piston Position Sensor Replacement (Service and Repair)
* Brake Pressure Modulator Valve Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for EBCM replacement, setup, relearn and programming