C1121
DTC C1120 or C1121
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 C1120 00
- Left Front Brake Hydraulic Circuit Blocked
DTC C1121 00
- Left Front Brake Hydraulic Circuit Leaking
Circuit/System Description
The electronic brake control module (EBCM) activates the valve relay to supply voltage to the valve solenoids. This voltage is referred to as the system voltage. The EBCM activates individual valve solenoids by grounding the valve solenoid control circuits. This verification is used to perform hydraulic checks at the normally open base brake valve, the front hydraulic circuit and the block.
Conditions for Running the DTC
* Ignition ON, accumulator pressure is less than 9,000 kPa (1,305 psi).
* The ignition voltage is greater than 10 volts.
* The EBCM performs a hydraulic system check every third ignition cycle.
* Brake pedal was depressed.
Conditions for Setting the DTC
C1120 00
This diagnostic detects if the left front circuit is blocked by actively applying pressure and monitoring the accumulator pressure change. The pressure change of the accumulator indicates the value of fluid used which is then compared to expected fluid used during a brake apply. Too little fluid usage indicates a blocked circuit.
C1121 00
This diagnostic detects if the left front circuit is leaking by actively applying pressure and monitoring the accumulator pressure change. The pressure change of the accumulator indicates the volume of fluid used which is then compared to expected fluid used during a brake apply. Too much fluid usage indicated a leaking circuit.
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 [1][2]Antilock Brakes / Traction Control Systems
Connector End View Reference
Component Connector End Views Connector Views
Description and Operation
ABS Description and Operation Description and Operation
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 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 high pressure accumulator 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 DTC C0277, C120C, C129A, C129B, C129D, C129E, C12B1, or C12F8 Antilock Brake System - Hybrid.
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.
6. Perform a hydraulic check, refer to Brake Hydraulic and Assist System Diagnosis (Two-mode Hybrid) Brake Hydraulic and Assist System Diagnosis (Two-mode Hybrid).
7. If the Brake Hydraulic and Assist System tests normal, replace the brake pressure modulator valve and verify DTC does not reset. If the DTC resets, replace the EBCM.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Brake Pressure Modulator Valve Replacement Service and Repair
* Control Module References Control Module References for EBCM replacement, setup, relearn and programming