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 Descriptors
DTC C0121
- Valve Relay Circuit




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 8 volts.



Conditions for Setting the DTC

One of the following conditions exists for 0.23 seconds:

* 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 antilock brake system (ABS).
* The ABS indicator turns ON.
* The dynamic rear proportioning (DRP) function is degraded.



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:

* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Circuit Testing (Component Tests and General Diagnostics)

Scan Tool Reference:

Control Module References (Programming and Relearning)


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.