U0121 on Chrysler: How to Diagnose & Fix
Lost Communication with ABS Module
1 Chrysler model · 1 documented issue · 1 critical · $300-$1,200 repair
U0121 on Chrysler by model: symptoms, diagnosis and fix
ABS control module suffers internal failures due to short circuits in main circuit board. Prevents proper ABS operation and stores fault codes. While regular braking functions, vehicle loses anti-lock capability, traction control, and stability control.
Common Symptoms
- ABS warning light constantly illuminated
- BAS warning light
- Traction control warning
- U0121 code (lost communication with ABS)
- No ABS function during hard braking
How to Fix
ABS module replacement or professional rebuild service. Check all wheel speed sensors and wiring before replacement. Many specialty shops offer rebuild for $300-500 with warranty. OEM module requires programming to VIN.
Sources for this issue (1)
U0121 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does U0121 mean on a Chrysler?
U0121 stands for "Lost Communication with ABS Module." U0121 is a network communication code meaning a control module on the vehicle's data bus has lost communication with the ABS (anti-lock brake system) module. Modern cars share information over a CAN bus, and when other modules stop receiving expected messages from the ABS unit, this code sets. Because the ABS module also handles traction control and stability control on most vehicles, you may see multiple warning lights and lost features. It points to a communication or power problem with the ABS module rather than a worn brake part. On Chrysler it is documented across 1 model: 300.
What are the most common causes of U0121?
The most common causes of U0121 are: Loss of power or ground to the ABS module, Blown fuse feeding the ABS controller, Damaged, corroded, or loose ABS module connector, Open, shorted, or chafed CAN bus wiring, Internal failure of the ABS control module, Corrosion or water intrusion in connectors/harness, Faulty gateway module disrupting bus communication. The specific cause varies by vehicle.
How much does it cost to fix U0121 on a Chrysler?
Published repair estimates on Chrysler range from $300 to $1,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for U0121 on a different make?
View U0121 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.