U0121
NetworkModule Communicationhigh severityLost Communication with ABS Module
What U0121 Means
Cannot communicate with the Anti-lock Brake System module.
Symptoms
- ABS light on
- Traction control disabled
- Stability control disabled
Common Causes
- ABS module power failure
- CAN bus wiring
- ABS module failure
- Fuse blown
Diagnostic Steps
- Check ABS fuses
- Test module power and ground
- Check CAN wiring
- Try direct communication
Where to start: Check fuses first. Common on water-damaged vehicles.
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