The U0402 DTC is triggered when the data coming from the TCM does not match the preprogrammed parameters. Basically, the engine control unit cannot understand what the transmission control module is saying.
What Transmission Do I Have?
How Serious is the Code?
The U0402 diagnostic trouble code is very serious, because the information coming from the TCM directly affects systems like the stability control and traction control systems.
Symptoms
Symptoms of a U0402 include:
- Erratic transmission behavior
- Limp Mode
Causes
- Damaged wiring
- Broken/corroded connectors
- Failed TCM
- Transmission failure
- ECU failure
How to Diagnose the Code?
The first step to diagnosing a U0402 OBDII trouble code, is to see if there are any manufacturer TSB’s related to this issue. If no known solutions are found, and the diagnostic process should start with a complete inspection of the wiring and connectors along the transmission wiring harness. If no damaged wires, connectors or bad ground connections are found, then the TCM and ECU should be tested. An internal mechanical inspection of the transmission may also be needed.
What Repairs Will Fix U0402?
- Repair or replace any damage wiring and connectors
- Replace TCM
- Replace ECU
- Install remanufactured transmission
Related Codes
N/A
What Transmission Do I Have?
