Circuit Description
The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage.
The electronic brake control module (EBCM) controls each solenoid valve by grounding the solenoid.
The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes:
| • | Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events. |
| • | Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events. |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C0121 Valve Relay Circuit
Conditions for Running the DTC
| • | The ignition voltage is greater than 10.5 volts. |
| • | The system relay is commanded ON. |
Conditions for Setting the DTC
The system voltage is less than 8 volts for 0.23 seconds.
Action Taken When the DTC Sets
If equipped, the following actions occur:
| • | The EBCM disables the DRP/ABS/TCS/VSES for the duration of the ignition cycle. |
| • | The ABS indicator turns ON. |
| • | The Traction Control indicator turns ON. |
| • | The DIC displays the Service Stability System message. |
| • | The EBCM will also set DTC C0281. |
| • | The red Brake warning indicator turns ON. |
Conditions for Clearing the DTC
| • | The condition for the DTC is no longer present and the DTC is cleared with a scan tool. |
| • | The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
Diagnostic Aids
The system relay is integral to the EBCM. The relay is not serviceable.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics Connector End View Reference: Antilock Brake System Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
Does the DTC reset as a current DTC? | -- | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections | |
3 |
Does the DMM display the specified value? | OL | Go to Step 5 | Go to Step 4 |
4 | Replace the electronic brake control module (EBCM) and the BPMV. Refer to Control Module References for replacement, setup and programming and Brake Pressure Modulator Valve Replacement . Did you complete the replacement? | -- | Go to Step 6 | -- |
5 | Replace the EBCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 6 | -- |
6 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
