U0101 Lost communication with TCM – a generic (SAE J2012) network code set when another module stops receiving data from the transmission control module.
Typical symptoms
- Gearbox in limp mode
- Gearbox warning on the cluster
- No gear display
Common causes
- Supply fuse, relay or earth fault at the transmission control module
- Corroded or loose connector
- Damaged CAN network wiring
- Low battery voltage or a recent voltage drop
- Internal failure of the transmission control module
Checks before suspecting the module
- Check battery voltage and charging
- Check the module fuses, supply and earth
- Inspect the connector for water and corrosion
- Check whether the module answers a scan tool
- If several modules are missing, measure the network wiring
If supply, earth and wiring are good and communication is still missing, the transmission control module may be faulty. Further diagnosis is needed before deciding to repair or replace it. See Gearbox & TCM repair.