U0121: Lost communication with ABS control module
Drive carefully. Get it checked within a week or two.
Can I drive with U0121?
Yes, but drive carefully and get it checked soon. ABS module offline; normal power brakes function, but ABS and traction control are offline.
What does U0121 mean?
U0121 stands for Lost Communication With Anti-Lock Brake System (ABS) Control Module.
Symptoms you may notice
- Multiple warning lights on dashboard simultaneously (ABS, CEL, Airbag)
- Speedometer or instrument cluster needles bouncing or freezing
- Transmission may shift harshly or default to safe limp gear
How much does it cost to fix?
Repair costs for code U0121 depend on the specific underlying root cause, ranging from simple DIY checks to component replacement. The table below lists the most common causes and rough price ranges in USD:
- Blown ABS power fuse (usually 40A or 50A fuse)
- Corroded ABS module electrical connector
- Failed Electronic Brake Control Module (EBCM)
- Broken CAN bus communication wire
What to do next
- Check ABS power fuses in the underhood fuse block.
- Inspect the large multi-pin plug connected to the ABS pump module.
- Drive with caution in wet or snowy weather.
Last updated: October 2026
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General guidance only, not a professional diagnosis. If the check-engine light is flashing, or the car is running rough, overheating or losing power, stop driving and get help.
About this code
Code U0121 indicates that the rest of the car has lost contact with the ABS computer. You will still have traditional hydraulic braking power, but without anti-lock pulsing during emergency stops. The car is safe to drive to a repair shop.