OBD-II code · Chassis
C0121 Valve Relay Circuit Malfunction
The ABS control module has detected a fault in the valve relay circuit, which supplies power to the ABS solenoid valves. With this fault, the module cannot energize the valves and ABS is disabled.
Is it safe to drive with C0121?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyValve relay failed
- PossibleInternal ABS module fault (relay integrated)
- Less likelyPower supply wiring or fuse fault
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Usually unaffected
- Parts involved
- ABS Valve Relay, ABS Control Module, ABS Hydraulic Unit
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.