Code
U0121
Network
Lost communication with ABS control module
Modules cannot communicate with the ABS controller over the network.
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Most likely causes
- ABS module power or ground fault
- CAN bus wiring fault
- Failed ABS module
Symptoms you may notice
- ABS/ESP lights
- Speedometer may fail
Checks to run
- Check ABS module power and grounds
- Test CAN wiring
- Scan ABS module
Tools you may need
Multimeter
OBD-II scanner
Always diagnose before replacing. Codes share symptoms; confirm the cause with measurements before buying parts.