U0121: Lost Communication With Anti-Lock Brake System (ABS) Control Module
System: Network / ABS · Priority: high
What U0121 means
The control module detected a condition matching the generic definition Lost Communication With Anti-Lock Brake System (ABS) Control Module. A trouble code identifies what the module detected; it does not automatically identify the failed part.
Useful next checks
- Check ABS module fuses, powers and grounds.
- Inspect network wiring and connectors.
- Scan other modules to determine whether the communication failure is isolated or network-wide.
Why vehicle context matters
The same generic code can have different diagnostic paths depending on engine, calibration, wiring layout, service bulletins and related codes. Freeze-frame and live data can help establish when the fault occurred.
Need a scanner for U0121?
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