U0121 Lost Communication With Anti-Lock Brake System (ABS) Control Module

Network Severity: High Generic OBD-II

A module cannot communicate with the ABS module.

Common causes

  • ABS module without power
  • Network wiring problem
  • Faulty ABS module

Symptoms

  • ABS and traction warning lights
  • Speedometer issues on some vehicles

What to check

  1. Check ABS fuses and grounds
  2. Check network wiring
  3. Have braking safety checked

Manufacturers may add their own detail to generic codes. If your vehicle shows a different description for U0121, follow the service information for that make and model.