U0121: Lost Communication with ABS Module
3 vehicles · 3 makes · $80-$3,200 repair
Most Reported On
U0121 is an OBD-II diagnostic trouble code meaning “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. This code is most commonly reported on 2005-2008 Dodge Magnum, 2007-2022 GMC Sierra 3500HD, and 2015-2020 Ford Transit, with repair costs ranging from $80 to $3,200.
Common Causes
Typical Repair Cost
Based on 5 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose U0121, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
As an Amazon Associate, we earn from qualifying purchases. Prices are approximate and may vary.
Vehicles Affected (3)
Front Differential Actuator Failure Causing 4WD Engagement Problems
Trailer brake controller / integrated trailer brake module malfunction
Electric power steering (EPS) assist loss / reduced assist warnings (new body style)
FAQ
What does U0121 mean?
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.
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?
Repair costs for U0121 range from $80 to $3,200, depending on the vehicle and root cause.
Which vehicles are affected by U0121?
Au7o has documented U0121 across 3 vehicle models from 3 manufacturers: Dodge, Ford, GMC.
Sources (11)
- NHTSADodge Magnum Electrical System Problems - NHTSA Complaints
- owner-reportDodge Magnum Reliability and Common Problems
- ForumSilveradoSierra: 2024 HD Trailer Brakes Disconnecting
- ForumGM-Trucks: 2024 Brake controller Problems
- ForumGrand Design Owners: Brake controller issues on 2024 GM HD trucks
- ForumDuramax Forum: 2024 HD trailer brake controller recall
- ForumSilveradoSierra: Electric Power Steering
- mediaZehl & Associates: 800,000 Chevrolet Silverado and GMC Sierra Trucks for Faulty Power Steering
- mediaAboutLawsuits: GMC Sierra, Chevy Silverado Recall Issued Due to Electric Power Steering Problems
- ForumSilveradoSierra: Loss of all power steering 2019 sierra elevation 5.3
- owner-reportCarComplaints.com — Ford Transit problem listings (owner-reported issues; check steering/EPS-related entries by model year)
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.