C0121

DTC C0121

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using the 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
- ABS Relay Circuit

Circuit/System Description

When the antilock brake system (ABS) is active, the valve relay provides voltage to actuate the solenoid valves. The valves do not use this voltage unless the ABS control module provides the ground for each solenoid coil.

Conditions for Running the DTC

* Vehicle speed is greater than 6 km/h (4 mph) with the brake pedal not applied.
OR
* Vehicle speed is greater than 15 km/h (9 mph) and the brake pedal is actuated.

Conditions for Setting the DTC

* The electronic brake control module (EBCM) is requesting valve activation and the relay output voltage is low.
* The EBCM is not requesting valve activation and the relay output voltage is B+.
* The EBCM detects 3 or more solenoid valve circuits are open or shorted during the self-test.
* A malfunction within the EBCM.

Action Taken When the DTC Sets

* The antilock brake system (ABS) is disabled.
* The ABS warning indicator turns ON.
* The electronic brake force distribution (EBD) is disabled.
* The EBD warning indicator turns ON.

If the failure is intermittent, the EBCM will enable the system at the next ignition cycle and set a history DTC.

Conditions for Clearing the DTC

The condition for setting the DTC is no longer present and the DTC is cleared with a scan tool.

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)
Electrical Information Reference

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

Scan Tool Reference

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

Circuit/System Testing

1. Ignition OFF, disconnect the EBCM connector.
2. Test for less than 5 ohm between ground and EBCM ground circuit terminals 13 and 26.

• If greater than the specified range, test for an open/high resistance in the ground circuit. If all circuits test normal, 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