C0121 BUICK – Valve Relay Circuit

C0121 BUICK Possible Symptoms

Anti-Lock Brake System (ABS) Warning Light ON,Engine Light ON (or Service Engine Soon Warning Light)

C0121 BUICK 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

C0121 BUICK Description

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.