U0129 code meaning
Lost Communication With Brake System Control Module A
Network system Generic code U01xx codes Check engine light
What U0129 means
U0129 points to the brake system control module A, in GM vehicles the OBD node with diagnostic ID 7E5. GM's 2019 LTG engine table checks frames $0C1, $0C5, $0D1, $1C6 and others every 500 ms (one of them 10 s) and needs two trips to set the MIL; the 2018 hybrid controller and the 2025 ECM treat it as Type A, the 2017 table as Special Type C. Stellantis calls the partner Brake System Control Module 1. GM N192267870 adds a software case: after a jump start the 2019 Silverado ECM stored U0129 with U0101/U0140 and lit the service engine lamp. U0121 covers the ABS module, U0418 invalid brake data. Brake assist and stop-start may be reduced.
U0129 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0129
- MIL or service engine lamp plus brake/ESC warnings
- Gear selection or stop-start blocked on some vehicles
- Several other U codes stored at the same time
Common causes of U0129
- Most likelyFuse, supply or ground of the brake control module faulty
- PossibleLow battery or jump start leaving stored network codes (ECM update released)
- PossibleDamaged or corroded CAN wiring to the brake module
- Less likelyBrake system control module internally faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake system control moduleCAN bus wiring
What each part of U0129 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 29 | The exact fault in that area. |
What to do next
- Note U0129 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0129
What does U0129 mean?
U0129 means "Lost Communication With Brake System Control Module A". U0129 points to the brake system control module A, in GM vehicles the OBD node with diagnostic ID 7E5. It is a generic code, so it means the same on every make.
Is it safe to drive with U0129?
Drive gently and only to a workshop. With U0129 the car can go into limp mode (reduced power) to protect itself.
Will U0129 fail an emissions test?
U0129 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0129 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U0129 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.