C0121

DTC C0121

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC C0121 00
- Valve Relay Circuit




Diagnostic Fault Information






Circuit/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

* The ignition is 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 turns ON.
* A malfunction DTC is set.
* The stability OFF indicator turns ON.
* The red BRAKE warning indicator could turn ON



Conditions for Clearing the DTC

* The condition for setting the DTC is no longer present.
* The EBCM automatically 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 ([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 (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Testing

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 (Verification Tests) after completing the diagnostic procedure.


Control Module References (Programming and Relearning) for EBCM replacement, setup, and programming