Lost Communication with TCM
The ECU has stopped receiving messages from the transmission control module. The transmission falls into limp-home mode (typically locked in 3rd or 4th gear), the speedometer may stop working, and shift adaptation freezes.
Affected components
- Tcm
- Can bus wiring
Common causes
- High likelihood: TCM unpowered or grounded poorly
- Medium likelihood: CAN wiring to TCM broken
- Low likelihood: Gateway module routing CAN messages incorrectly
Possible 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
Diagnostic notes
- The malfunction indicator lamp may illuminate
- Reduced-power or limp mode may occur
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.