U0402
Invalid Data Received from TCM
A control module is communicating with the transmission control module but receives implausible data — wrong checksum, frozen value, or out-of-range value. Often results in transmission limp-home.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
Ordered by how often each turns out to be the cause.
- TCM software bug or outdated calibrationPossible
- TCM internal sensor or processing faultPossible
- CAN corruption causing checksum errorsPossible
Parts involved
- TCM
- CAN Bus Wiring
U0402 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.