OBD-II code · Network
U0121 Lost Communication with ABS Control Module
The CAN messages from the ABS module are missing. ABS, ESP/ESC and traction control all become inactive (warning lamps illuminate), the speedometer may go to zero on cars that derive vehicle speed from the ABS module, and adaptive cruise control is disabled.
Is it safe to drive with U0121?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyABS module unpowered (often a corroded ground or fuse)
- PossibleCAN wiring to ABS broken
- PossibleABS module failed
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–6 h
- Emissions test
- Usually unaffected
- Parts involved
- ABS Control Module, Can Bus Wiring
Related codes
- U011ELost Communication With Throttle Actuator B Control Module
- U011FLost Communication With V2X Module
- U0120Lost Communication with Starter/Generator Control Module
- U0122Lost Communication with Vehicle Dynamics Control Module
- U0123Lost Communication with Yaw Rate Sensor Module
- U0124Lost Communication with Lateral Acceleration Sensor Module
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.