Fault code P0702 – a step-by-step guide to diagnosing and fixing it

Error code P0702 is displayed and the check engine light is on - what does this mean?

DTC P0702 is detected by the OBD system when there is an electrical problem in the transmission control module (TCM) or its circuits. This fault code indicates a malfunction in the transmission of signals between the transmission control module and other vehicle systems. The exact definition may vary slightly between manufacturers, but generally refers to electrical problems in the automatic transmission control system.

What can cause this error code?

• Defective transmission control module (TCM)
• Damaged cable connections to the transmission control unit
• Corroded or loose plug connections
• Short circuit in the transmission control unit
• Defective fuses in the transmission control circuit
• Faulty earth connections
• Damaged wiring harnesses
• Voltage problems in the vehicle electrics
• Defective relays in the transmission system

What symptoms occur in parallel with fault code P0702?

• Shifting problems: The automatic transmission shifts irregularly or gets stuck in a gear. Emergency running program: The transmission switches to emergency running mode and limits the available gears. Jerking when changing gear: Noticeable jolts or delays when changing gear. Loss of power: Reduced engine power and poor acceleration. Starting problems: In rare cases, the vehicle may fail to start. Warning lights: In addition to the engine warning light, the transmission warning light may also come on.

How can the problem of error code P0702 be rectified?

• The repair requires a systematic diagnosis of the electrical components in the transmission system.
• Complete check of all plug connections: Disconnect, clean and firmly reconnect all connectors on the transmission control module, checking for corrosion or damage
• Replace the transmission control module: If the TCM is defective, replace the entire control unit and then have it programmed
• Repair the cable connections: Locate damaged cables to the transmission control unit and replace with new cables
• Check and replace the fuses: Check all relevant fuses in the transmission control circuit and replace defective ones
• Replace earth connections: Clean all ground points of the transmission system and lay new ground cables if necessary
• Check the power supply: Check battery voltage and alternator output, replace defective components if necessary