The vehicle’s modules (ECU/PCM, ABS, BCM, etc.) communicate through the CAN bus network. Code U0101 is stored when the ECM/PCM can’t communicate with the TCM. This usually means either the TCM is offline, the wiring is faulty, or there’s a network issue.
1. Faulty TCM (internal failure)
2. Blown fuse or relay supplying power to TCM
3. Damaged/corroded wiring or connectors in CAN bus lines (CAN+ / CAN–)
4. Poor ground connection to TCM
5. Software corruption in TCM
6. Low battery voltage or unstable power supply
1. Check Engine Light (CEL)
2. Transmission stuck in limp mode (usually 2nd or 3rd gear only)
3. Harsh or no shifting
4. Speedometer/gear indicator not working properly
5. Engine may run, but transmission doesn’t respond normally
1. Check TCM fuse & relay – replace if blown.
2. Inspect wiring harness & connectors – especially CAN lines near transmission.
3. Check grounds – clean and tighten TCM ground points.
4. Check battery/charging system – low voltage often causes comm errors.
5. Reprogram or replace TCM if communication cannot be restored.
Copyright © All Rights Reserved by SEHMBI