C0121

DTC C0121 Valve Relay Circuit Malfunction

Steps 1-9:

Circuit Description
When the 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 DTC will also set if the ABS control module detects three or more solenoid valve circuits are open or shorted during the self-test.

Diagnosis
This procedure checks whether there is a poor ground connection for the Electronic Brake Control Module (EBCM).

Cause(s)
- A connector terminal is corroded.
- The wiring harness is damaged.
- The ground terminal is not conducting properly.
- The EBCM is defective.

Fail Action
ABS/EBD is disabled, and the ABS / EBD warning lamp is turned ON for the remainder of the ignition cycle. If the failure is intermittent, the control module will enable the system at the next ignition cycle and set a history DTC C0121.

Diagnostic Aids
It is very important to perform a thorough inspection of the wiring and the connectors. Failure to do so may result in misdiagnosis, causing part replacement with reappearance of the malfunction.