U0304 — Invalid Data Received from Transmission Control Module
The ECU receives messages from the TCM but their content is implausible (e.g. invalid gear, impossible speed). The transmission may switch to limp-home mode and shift quality is degraded.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Tcm
- Can bus wiring
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Software version mismatch after replacement
- TCM partially failing
- 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
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
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.