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.
Medium severity. Can I keep driving?It depends on which control module has dropped out. If it affects the engine, brakes, or steering, do not continue your trip: call for roadside assistance.
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
Most likely causes
- TCM software bug or outdated calibration
- TCM internal sensor or processing fault
- CAN corruption causing checksum errors
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
What each character of U0402 means
- U: Communication network
- 0: Generic code: same on every make
- 4: Subsystem depends on the code range
- 02: Specific fault in that system
Frequently asked questions
Can I keep driving with code U0402?
It depends on which control module has dropped out. If it affects the engine, brakes, or steering, do not continue your trip: call for roadside assistance.
What causes code U0402?
The most common causes are: tCM software bug or outdated calibration; tCM internal sensor or processing fault; cAN corruption causing checksum errors.
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.