U0129
Lost Communication With Brake System Control Module A
Communication / brakes
Generic OBD-II
High
What it means
U0129 sets when a module loses communication with the brake system control module (the ABS/ESC controller). Your base hydraulic brakes still function, but anti-lock braking, traction control, and electronic stability control usually switch off, and their warning lights come on. On some vehicles this also affects features that rely on wheel-speed data.
High
Can I keep driving? Your normal hydraulic brakes still work, but ABS, traction, and stability control are likely disabled — drive gently, avoid hard or slippery stops, and repair promptly.
Common symptoms
What you'll notice
- ABS, traction control, and stability control warning lights on
- Those systems disabled (no ABS on hard braking)
- Speedometer or wheel-speed-based features may be affected on some vehicles
- Brake module unreachable by a scan tool
Common causes
Most likely first
- Damaged wiring or connector at the ABS/brake control moduleLikely
- Loss of power or ground to the brake moduleCommon
- CAN bus fault between the brake module and other controllersCommon
- Failed brake system control moduleLess often
- Corrosion or water intrusion at the module connectorLess often
How to diagnose & fix
Work through it in order
- Scan all modules and confirm whether the brake module responds.
- Inspect the brake module's connector, power, and ground.
- Check the CAN wiring between the brake module and the network for opens or shorts.
- Verify proper power and ground at the module with a meter.
- If wiring and power check out, the brake control module may need replacement and programming. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with U0129?+
Only with caution — you keep basic braking but lose ABS and stability control, which matter in emergency or slippery stops. Fix it soon.
Can I just clear U0129?+
It clears but returns until the module is communicating again; this needs the wiring or module repaired.
Related codes
Often seen with U0129
Read & clear U0129 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX