C0121

DTC C0121

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using the diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)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 is disabled.

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 (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
* Connector Repairs (Connector Repairs)

Scan Tool Reference

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

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the EBCM.
2. Test for less than 5 ohm between the ground circuits listed below and ground:

* Terminal 13
* Terminal 26

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

3. Ignition ON, verify that a test lamp illuminates between the B+ circuits listed below and ground:

* Terminal 1
* Terminal 14

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, replace the brake pressure modulator valve and EBCM assembly.

4. If all circuits test normal, replace the brake pressure modulator and EBCM assembly.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Control Module References (Programming and Relearning)for brake pressure modulator valve and EBCM replacement, programming and setup