Valve Relay Circuit
Table of contents
C0121 GMC 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
How do I fix code C0121 GMC?
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins.
Cost of diagnosing the C0121 GMC code
The cost of diagnosing the C0121 GMC code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle’s make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
Possible Symptoms
- Anti-Lock Brake System (ABS) Warning Light ON
- Engine Light ON (or Service Engine Soon Warning Light)
C0121 GMC 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.