C0121 Code: Meaning, Causes, and Symptoms | OBD2 Codes
C0121 – Valve Relay Circuit
C0121 Possible Symptoms
Anti-Lock Brake System (ABS) Warning Light ON,Engine Light ON (or Service Engine Soon Warning Light)
C0121 Possible Causes
Faulty Electronic Brake Control Module (EBCM),Electronic Brake Control Module (EBCM) harness is open or shorted,Electronic Brake Control Module (EBCM) circuit poor electrical connection
The system relay is energized when the ignition is ON. The system relay supplies voltage to the solenoid valves and the pump motor. This voltage is referred to as the system voltage. The Electronic Brake Control Module (EBCM) controls each solenoid valve by grounding the solenoid. The EBCM controls the pump motor by grounding the control circuit. The pump serves 2 purposes: – Transfers brake fluid from the brake calipers to the master cylinder reservoir during pressure decrease events. – Transfers brake fluid from the master cylinder reservoir to the brake calipers during pressure increase events.