OBD-II · Network and communication (U)
U0101
Lost communication with transmission control module (TCM)
What it means
Another module has stopped receiving messages from the automatic gearbox control unit.
Symptoms
- Gearbox warning light
- Gearbox stuck in one gear (limp mode) or no drive
- Harsh or no shifting
- Gear indicator missing on the dash
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | weak 12V battery or poor earth |
| 02 | blown gearbox ECU fuse |
| 03 | corroded or loose gearbox control unit connector (on DSG/dual-clutch boxes the unit is inside the mechatronic unit) |
| 04 | damaged CAN wiring to the gearbox |
| 05 | failed gearbox control unit or mechatronic unit |
What to check, step by step
- 01Check 12V battery and main earths
- 02Check gearbox control unit fuse and power/ground supply
- 03Check whether the gearbox module answers a scan tool
- 04Inspect the gearbox connector for oil wicking, corrosion or bent pins
- 05Test CAN wiring to the gearbox before condemning the control unit