The Lemon IndexThe other computers in the car stopped hearing from the anti-lock brake (ABS) module.
Stop and fix now. Don't put it off. This can affect safety, stall the car or cause expensive damage.
Wiring or connector fault on the data network. Then: power or ground problem at the anti-lock brake (ABS) module; failed anti-lock brake (ABS) module.
Owners named U0121 in 40 complaints to the U.S. government, most often on the Chevrolet Malibu.
Cars owners report it on
Complaints that name U0121, by model. Raw counts, not a failure rate: popular models get more complaints.
Years owners report it on most: 2006 Toyota RAV4 · 2014 Chevrolet Malibu · 2020 Chevrolet Malibu · 2024 Ford F-Series
The details
What U0121 means
The other computers in the car stopped hearing from the anti-lock brake (ABS) module. Features that depend on it can stop working, and several warning lights often come on together.
Can I drive with U0121?
Stop and fix now. Don't put it off. This can affect safety, stall the car or cause expensive damage.
65% of the owner complaints that name U0121 also say the car brakes or ABS act up. A complaint can describe more than one problem, so this doesn't prove the code caused it.
Common causes of U0121
- Wiring or connector fault on the data network
- Power or ground problem at the anti-lock brake (ABS) module
- Failed anti-lock brake (ABS) module
- Weak battery
A shop should confirm the cause with a scan and tests before replacing parts.
What owners describe
- Brakes or ABS act up: 65% of complaints
- Warning lights and electrical faults: 35% of complaints
- Stalls or shuts off: 25% of complaints
- Loses power or goes into limp mode: 22% of complaints
Share of complaints naming the code whose text also mentions each problem.
Model years that report U0121 most
2006 Toyota RAV4 (2), 2014 Chevrolet Malibu (2), 2020 Chevrolet Malibu (2), 2024 Ford F-Series (2).
Related codes
U0122 U0126 U0129 U0111 U0131 U0109 U0104 U0103
Quick answers
What does U0121 mean?
Lost Communication With Anti-Lock Brake System (ABS) Control Module. The other computers in the car stopped hearing from the anti-lock brake (ABS) module. Features that depend on it can stop working, and several warning lights often come on together.
Can I drive with U0121?
Stop and fix now. Don't put it off. This can affect safety, stall the car or cause expensive damage.
What causes U0121?
Wiring or connector fault on the data network; Power or ground problem at the anti-lock brake (ABS) module; Failed anti-lock brake (ABS) module; Weak battery.
Counts: NHTSA owner complaints whose text names U0121. A complaint is an owner's report, not a diagnosis. Meanings: the standard SAE J2012 definitions in our own words; manufacturer codes only where verified for that make. General information, not repair advice for your car.