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 Hybrid/EV Battery Pack X1 A4
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 brake sensor performance procedure. It is recommended that a charger/maintainer or equivalent be used to maintain proper battery voltage during this procedure.

1. Place the power button in the ON/RUN position.
2. Place the transmission in PARK.

Note: Do not depress the brake pedal during the EBCM relearn.

3. Using a scan tool access the EBCM, Configuration/Reset Functions, EBCM Relearn. The EBCM relearn procedure will verify valve and pressure sensor calibrations are correct.

Note: To ensure the complete brake modulator and high pressure accumulator (HPA) pressure relief procedure is allowed to occur; the brake controller must see 1 pedal apply with the propulsion system enabled, followed by a proper shutdown without applying the brake pedal.

4. Enable the propulsion system.
5. Apply and release the brake pedal.

Note: The power button must be in the OFF position, and without applying the brake pedal to ensure the brake modulator and high pressure accumulator (HPA) pressure relief occurs. This process will take approximately 1-3 minutes.

6. Place the power button in the OFF position, without applying the brake pedal.
7. Remove the remote keyless entry (RKE) transmitter and close all of the vehicle doors.
8. Wait approximately 1-3 minutes until the brake modulator and the high pressure accumulator (HPA) pressure relief is complete.

Note: The power button must remain in the ON/RUN position, with the engine OFF during the remainder of this diagnostic procedure, unless otherwise instructed.

9. Place the power button in the ON position, engine OFF, and do not apply the brake pedal.
10. Using the scan tool, select Data Display for the EBCM, scroll through the data list, select and accept the following:

* Master Cylinder Pressure Sensor
* Rear Brake Pressure Sensor
* Brake Pressure Sensor
* Accumulator Pressure Sensor
* Brake Controls Brake Pedal Position Sensor 5 V Reference
* Brake Controls Brake Pedal Position Sensor Input A
* Brake Controls Brake Pedal Position Sensor Input B

11. Power button ON, engine OFF, brakes not applied, verify the following sensor parameters are within the specified values:

* Brake Controls Brake Pedal Position Sensor 5 V Reference - Between 4.75-5.25 V
* Brake Controls Brake Pedal Position Sensor Input A - Between 0.4-0.8 V
* Brake Controls Brake Pedal Position Sensor Input B - Between 4.2-4.6 V

• If any of the parameters are not within the specified range, refer to DTC C029C, C120C, C129A-C129F, C12B1, or C12F8 C029C.

12. Power button ON, engine OFF, brakes not applied, verify the following sensor parameters are within the specified values:

* 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 Q5 brake pressure modulator valve.

13. Perform a hydraulic check, refer to Brake Hydraulic and Assist System Diagnosis Brake Hydraulic and Assist System Diagnosis.
14. If the Brake Hydraulic and Assist System tests normal, replace the Q5 brake pressure modulator valve and verify DTC does not reset. If the DTC resets, replace the K17 EBCM.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Electronic Brake Control Module with Brake Pressure Modulator Valve Replacement Electronic Brake Control Module with Brake Pressure Modulator Valve Replacement
* Control Module References Control Module References for EBCM replacement, programming and setup