U0101: Lost Communication With TCM

Short answer: U0101 means “Lost Communication With TCM”. It is a standard OBD-II code, so the basic meaning is the same on every car. Below is what it means on each of the 6 cars we cover, with a link to the full page for each car.

Standard OBD-II code Same meaning on all cars (SAE J2012).

U0101 on each car

Symptoms

1. Check engine light on
2. Vehicle will not shift
3. Vehicle stays in one gear (usually 2nd or 3rd)

Likely causes

1. Typically the causes for this code to set are
2. Open in the CAN bus + circuit
3. Open in the CAN bus - circuit
4. Short to power in either CAN bus circuit
5. Short to ground in either CAN bus circuit
6. Rarely - faulty control module

What to check, in order

1. Check battery voltage and the main fuses
2. Check the connectors of the module named in the code
3. Read codes from all modules with a capable scanner

Causes and checks above are the general meaning. The exact test steps and values differ by car: open your car’s page.

All fault codes