Fault-Code Library · Vehicle network
U0121: Lost communication with ABS control module
Modules on the vehicle network are not receiving expected messages from the ABS or stability-control controller.
Common symptoms
- •ABS warning
- •Stability-control warning
- •Speedometer issues
- •Multiple network codes
Likely causes
- •Low battery voltage
- •ABS module power or ground fault
- •CAN wiring issue
- •Water ingress or module failure
First checks
- •Test battery and charging health
- •Check ABS module powers, grounds, and fuses
- •Inspect wheel-arch and module-area wiring for damage or water
Important
ABS communication faults can affect braking assistance and stability functions, so diagnose before normal use.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.
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