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.

Real-world scan data

Seen in

665

scans in the past year

Found in

0.1%

of scans

0.2%

of scans that found faults

Appears alongside · share of U0129 scans

U0100in 43.8% of scans

U0151in 13.7% of scans

B1660in 13.5% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear U0129 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX