What usually causes it
- A damaged wire or a loose, rusty plug on the network line
- A blown fuse for the ABS computer
- A weak battery or a bad ground
- A failed ABS computer
U0121Starts at: Get it checked this week
Lost contact with the anti lock brake (ABS) computer
Other computers in the car cannot talk to the ABS computer, which runs the anti lock brakes and stability control. Those systems may not work, so the car could skid more easily on wet or icy roads.
Check this first
Check that the battery cables are tight and clean, and look at the ABS fuses in the fuse box.
What to watch for
- The ABS or brake warning light is on. A red brake light or a soft brake pedal means stop right away
- The wheels lock up or the car skids when you brake hard
- The stability control or traction control light is on
Can I keep driving?
We rate U0121 as Get it checked this week. It is not an emergency yet, but it can get worse. If the light starts flashing, stop driving soon.
Quick answers about U0121
What does U0121 mean?
Lost contact with the anti lock brake (ABS) computer. Other computers in the car cannot talk to the ABS computer, which runs the anti lock brakes and stability control. Those systems may not work, so the car could skid more easily on wet or icy roads.
Can I keep driving with U0121?
We rate U0121 as Get it checked this week. It is not an emergency yet, but it can get worse. If the light starts flashing, stop driving soon.
What usually causes U0121?
The most common causes, in order: A damaged wire or a loose, rusty plug on the network line; A blown fuse for the ABS computer; A weak battery or a bad ground; A failed ABS computer.
Estimates only. A mechanic should confirm. The same code can mean slightly different things on different cars; the app explains it for your exact year, make, model and mileage.