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.

DTC C0121 will set if the valve relay voltage is low or if the relay supply line is at 12 volts when the ABS control module is not requesting it. This diagnostic trouble code (DTC) will also set if the ABS control module detects 3 or more solenoid valve circuits are open or shorted during the self-test.

This procedure checks whether there is a poor ground connection for the electronic brake control module (EBCM).

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

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

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Electronic Brake Control Module Scan Tool Information

1. Ignition OFF, disconnect the EBCM connector.
2. Measure for 0 ohms between the EBCM ground circuits and ground.

⇒	If more than 0 ohms, repair open or high resistance in ground circuit.

⇒	If all circuits test normal replace the EBCM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for EBCM and BPMV replacement, setup, and programming