OBD2 fault code
Very highU0121
Lost Communication With ABS Control Module
The code identifies an implausible condition in the monitored system. The component named in the code is not automatically the defective part.
What does U0121 mean?
Lost Communication With ABS Control Module. The engine or vehicle control system detected that a measured value, control response, or communication signal was outside the expected range.
Common symptoms
- multiple warning lights at once
- functions such as ABS, ESC, or engine control unavailable
- diagnostic access to individual modules fails
Likely causes
- vehicle voltage too low
- CAN wiring, connector, or termination fault
- affected module lacks power or has an internal fault
Sensible diagnostic order
- check battery and charging voltage first
- inspect module fuses, ground, and power supply
- professionally measure CAN bus and review related U-codes
Can I continue driving?
Stop if warning lights, power loss, or rough running occur. If the check-engine light flashes, the engine shakes strongly, warning messages increase, or power drops significantly, stop and arrange professional assistance.
This information is a diagnostic aid and does not replace inspection by a qualified workshop. Manufacturer-specific definitions may differ.
FAQ
Can I continue driving with U0121?
Stop if warning lights, power loss, or rough running occur.
Does U0121 always identify a defective part?
No. A fault code identifies a monitored system or implausible condition. Wiring, voltage, leaks, and related components must also be checked.
How can DiagnostiX help with U0121?
DiagnostiX reads the code from the vehicle, assigns it to the vehicle profile, and displays relevant live values and a structured explanation.