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U0402 — Invalid Data Received From Tcm

Generic OBD-II · all makesNetwork / communication

Code U0402 indicates that the Engine Control Module (ECM) has received data from the Transmission Control Module (TCM) that is logically incorrect or out of the expected range. Unlike a total loss of communication, the modules are still talking, but the information being transmitted is invalid.

Symptoms

What causes it — most likely first

1. TCM Internal Failure

The Transmission Control Module has an internal electronic fault causing it to send corrupted or illogical data packets.

2. Wiring Harness Damage

Frayed, shorted, or corroded CAN bus wiring between the TCM and PCM causing signal interference.

3. Voltage Instability

A failing battery or alternator creating voltage spikes or drops that distort module communication.

4. Faulty Transmission Sensors

A failing speed or pressure sensor providing incorrect data to the TCM, which then relays invalid information to the ECM.

5. PCM/ECM Software or Hardware Fault

The engine computer is unable to correctly interpret valid data from the TCM due to an internal processing error.

How it's diagnosed

  1. Scan for additional diagnostic trouble codes in both the ECM and TCM to identify the root fault.
  2. Verify battery voltage and charging system output to ensure stable power supply to modules.
  3. Inspect the wiring harness and connectors for corrosion, rubbing, or broken wires between the PCM and TCM.
  4. Check transmission fluid levels and condition to rule out mechanical faults triggering illogical sensor data.
  5. Perform a pin-out test on the CAN bus network to check for proper resistance and continuity.
  6. Check for available manufacturer software updates for the TCM or PCM.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0400 — Invalid Data ReceivedU0401 — Invalid Data Received From EcmpcmU0403 — Invalid Data Received From Transfer CaU0404 — Invalid Data Received From Gear Shift U0405 — Invalid Data Received From Cruise ContU0406 — Invalid Data Received From Fuel Inject

Frequently asked

Does this code mean my transmission is mechanically broken?

Not necessarily. U0402 is an electronic communication code; while mechanical failure can cause the TCM to send odd data, the issue is often electrical or software-related.

Should I replace the PCM to fix this code?

No. It is common for drivers to be told to replace the PCM, but this is rarely the cause. The TCM or the wiring harness is significantly more likely to be the source of invalid data.

Is this different from a 'Loss of Communication' code?

Yes. A loss of communication code (like U0101) means the modules aren't talking at all. U0402 means they are talking, but the TCM is saying something that doesn't make sense to the PCM.