Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC C0121 00: Valve Relay CircuitCircuit/System Description
An internal solenoid valve relay in the electronic brake control module (EBCM) supplies battery positive voltage to all solenoid valves. This voltage is referred to as system voltage. The EBCM activates the solenoid valve relay when the ignition is turned ON. Once the solenoid valve relay has been activated, the EBCM supplies ground to actuate individual solenoid valves.
Conditions for Running the DTC
| • | Ignition ON. |
| • | Ignition voltage is greater than 9 volts. |
Conditions for Setting the DTC
| • | The EBCM commands the solenoid valve relay on and battery voltage is not present at the solenoid valves. |
| • | The EBCM commands the solenoid valve relay off and battery voltage is present at the solenoid valves. |
Action Taken When the DTC Sets
| • | The EBCM disables the ABS/traction control system (TCS)/vehicle stability enhancement system (VSES) dynamic rear proportioning (DRP) for the duration of the ignition cycle. |
| • | The ABS indicator illuminates. |
| • | The stability OFF indicator illuminates. |
| • | The red BRAKE warning indicator could illuminate. |
Conditions for Clearing the DTC
| • | The condition for setting the DTC is no longer present. |
| • | The EBCM clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
Diagnostic Aids
The solenoid valve relay is integral to the EBCM. The relay is not serviceable.
Reference Information
Schematic Reference
Antilock Brake System Schematics
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Clear the DTC. Cycle the ignition OFF and ON. Operate the vehicle. Verify that DTC C0121 does not reset.
| ⇒ | If DTC C0121 resets, replace the EBCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for EBCM replacement, setup, and programming
