U0121Network
CAN network · SAE
Lost Communication With ABS Module
Meaning
The ECU has lost communication over the data network with the ABS/ESP module. Without the ABS data (wheel speeds, system status) many safety and control functions are limited.
Common causes
- CAN wiring to the ABS broken or shorted
- Corroded or loose ABS module connector
- Missing ABS power supply or ground
- Faulty ABS module
- Network disturbance from another faulty module
Symptoms
- ABS, ESP and brake lights on
- Possible check engine light and wrong speedometer
- Braking aids disabled
- Several modules with lost-communication codes
Severity
Serious: disabled ABS and ESP reduce safety under braking and in corners; act immediately.
What to do
- Check the ABS module's power supply and ground
- Check continuity and resistance of the CAN wires to the ABS
- Inspect connectors for corrosion and moisture
- Isolate the disturbing module if the fault is widespread