Trouble code
U0121
Lost Communication With ABS Control Module
What U0121 means
The ABS module has dropped off the vehicle network.
Symptoms you may notice
- ABS and traction lights
- Speedometer may stop working
- Harsh shifting
Common causes, cheapest first
- Low system voltage
- Corroded ABS module connector
- Damaged bus wiring
- Failed ABS module
Before you buy anythingCheck charging system voltage first. Modules drop off the bus when voltage sags, and replacing an ABS module you did not need is an expensive mistake.
What to do next
- Confirm the code with your own scan tool, or have it read free at a chain parts store.
- Decode your VIN so you know your exact engine and build date.
- Work down the causes above from cheapest to most expensive.
- Search NHTSA for a recall or service bulletin covering this symptom on your vehicle.
- Read the brakes buying guide before ordering.
U0121 is a generic OBD-II code, standardized across every make and model sold in the US from 1996 onward. The meaning is the same on any vehicle; the specific part and its location are not.
Parts
Parts commonly needed for U0121
These go to Amazon. We earn a commission if you buy, at no extra cost to you — see our affiliate disclosure. Which one you actually need depends on diagnosis — read the note above first.
Confirm fitment against your VIN on the listing page before ordering. A part that matches your year and model can still be wrong for your build date or engine code.