U029B code meaning
Lost Communication With Drive Motor Control Module C
What U029B means
Drive motor control module C is the inverter and controller of a third traction motor, so it only occurs on vehicles with three or four drive motors. Production examples are the tri-motor version of the GMC Hummer EV, which drives its rear axle with two motors, and Rivian's quad-motor R1T and R1S with one motor per wheel. U029B is stored when the propulsion or vehicle controller stops receiving any periodic messages from module C. Frames that still come but carry unusable values are U059C; U0292 and U029C cover the second and fourth motor controllers. Which motor gets letter C is the maker's decision, and no manufacturer documents U029B publicly. For hybrids, CARB 1968.2 demands that missing communication from digital inputs be detected. Expect that motor to be shut off and reduced power and traction.
U029B at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U029B
- Reduced power warning, one motor disabled
- Torque vectoring or all-wheel-drive functions unavailable
- Drive system warning in the cluster
Common causes of U029B
- PossibleFuse, low-voltage supply or ground of module C faulty
- PossibleDamaged or corroded bus wiring or connector at the drive unit
- PossibleSoftware fault or interrupted programming of module C
- Less likelyDrive motor control module C internally failed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Drive motor control module cVehicle bus wiring
What each part of U029B means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9B | The exact fault in that area. |
What to do next
- Note U029B 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 U029B
What does U029B mean?
U029B means "Lost Communication With Drive Motor Control Module C". Drive motor control module C is the inverter and controller of a third traction motor, so it only occurs on vehicles with three or four drive motors. It is a generic code, so it means the same on every make.
Is it safe to drive with U029B?
Drive gently and only to a workshop. With U029B the car can go into limp mode (reduced power) to protect itself.
Will U029B fail an emissions test?
U029B 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 U029B to fix?
Difficulty: workshop only. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will U029B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.