Volt

DTC C1120 or C1121

The electronic brake control module activates the valve relay to supply voltage to the valve solenoids. This voltage is referred to as the system voltage. The electronic brake control module 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.

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.

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

ABS Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Note: The 12 V 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. Vehicle in Service Mode with the transmission in PARK.

Note: Do not depress the brake pedal during the Electronic Brake Control Module Learn procedure.

2. Perform the Electronic Brake Control Module Learn procedure with a scan tool.

Note: To ensure the complete brake modulator and high pressure accumulator 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.

3. Vehicle ON, apply and release the brake pedal.

Note: Vehicle OFF, without applying the brake pedal ensure the brake modulator and high pressure accumulator pressure relief occurs. This process will take approximately 1-3 minutes.

4. Vehicle OFF, without applying the brake pedal.
5. Remove the remote keyless entry transmitter and close all of the vehicle doors. Wait approximately 1-3 minutes until the brake modulator and the high pressure accumulator pressure relief is complete and the vehicle powers down.
6. Vehicle ON, brakes not applied.
7. Verify the scan tool parameters listed below are within the specified range:

•	Brake Controls Brake Pedal Position Sensor 5 V Supply Voltage - Between 4.75-5.25 V

•	Brake Controls Brake Pedal Position Sensor Circuit 1 - Between 1.4-1.7 V

•	Brake Controls Brake Pedal Position Sensor Circuit 2 - Between 58-78%

⇒	If any parameter is not within the specified range

Refer to DTC C029C, C120C, C129A-C129F, C12B1, or C12F8 .

⇓	If all parameters are within the specified range

8. Vehicle ON, brakes not applied.
9. Verify the scan tool parameters listed below are less the specified range:

•	Brake Master Cylinder Pressure Sensor - Less than 100 kPa (15 psi)

•	Brake Pressure Sensor - Less than 100 kPa (15 psi)

•	High Pressure Accumulator Sensor - Less than 800 kPa (116 psi)

⇒	If any parameter is greater than the specified range

Replace the Q5 brake pressure modulator.

⇓	If all parameters are less than the specified range

10. Perform a brake hydraulic system test, refer to Brake Hydraulic and Assist System Diagnosis .

⇒	If the brake hydraulic system test does not pass

Repair as necessary.

⇓	If the brake hydraulic system tests normal

11. Replace the Q5 brake pressure modulator.
12. Verify the DTC does not set while operating the vehicle under the Conditions for Running the DTC.

⇒	If the DTC sets

Replace the K17 electronic brake control module.

⇓	If the DTC does not set

13. All OK.

Perform the Diagnostic Repair Verification after completing the repair.