CAN network

U0251 — Lost Communication with Telematics Control Module

Severity: low Safe to drive

What U0251 means

A control module stopped receiving messages from the telematics module over the CAN bus. This module handles connected features such as emergency calls, remote access, and vehicle data transmission. Normally it exchanges data with other modules constantly, and when it stops responding U0251 is stored.

Symptoms

  • Connected services unavailable
  • SOS button does not respond
  • Other warning lamps may come on
  • Features handled by the module do not work
  • Remote start or phone app control fails

Possible causes

  1. Failed telematics module
  2. Damaged antenna or antenna cable
  3. CAN wiring open, shorted, or chafed
  4. Corroded connector or terminals
  5. Lost power or ground at the module
  6. Another faulty module loading the bus
  7. Low battery voltage

How to diagnose

  1. Run a full-module scan and map which modules are not communicating
  2. Check battery voltage and terminal condition
  3. Check the fuses and relays that power the telematics module
  4. Inspect the module connector and harness for corrosion, moisture, and chafing
  5. Test power and ground at the module connector with a multimeter
  6. Measure CAN bus resistance and voltages at the diagnostic connector (about 60 ohms between CAN-H and CAN-L is typical)
  7. Inspect the antenna and its cable
  8. If needed, unplug suspect modules one at a time, only following the documented procedure

Common fixes

  • Repair the damaged CAN wire or connector
  • Clean corrosion and restore the module's power and ground
  • Replace or reprogram the telematics module
  • Replace the antenna or its cable
  • Replace the module that is disrupting the bus

Questions and answers

What does U0251 mean?

It means other modules lost communication with the telematics module on the CAN bus. The cause may be the module itself, its power, or the wiring.

Is U0251 caused by an expired OnStar subscription?

No, a lapsed subscription does not set this code. It points to a hardware or electrical communication problem.

Can I drive with U0251?

Usually yes, but emergency services may be unavailable. It is best not to postpone diagnosis for long.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.