Engine Running with Key Off, Continuous Run (Install Diode to Relay/Solenoid)

Some customers may comment on the engine running for 10-15 seconds with the key off.

These vehicles may be equipped with aftermarket equipment controlled by a large relay or solenoid. If the solenoid or relay is wired into the run/crank circuit of the vehicle, large negative voltage spikes can occur at its positive terminal when the relay or solenoid is de-energized (keyed-off). These spikes can permanently damage the internal circuitry of the TCM. Once damaged, it is possible for the Transmission Control Module (TCM) to pass retained accessory power onto the run/crank circuit keeping the Engine Control Module (ECM) on until retained accessory power goes low.

Important: DO NOT replace the TCM until the root cause of the condition has been identified to the relay/solenoid negative voltage spikes.

To prevent damage to additional TCMs, the relay or solenoid must have the control circuit suppressed with a diode. The diode will prevent the negative voltage spikes from being transmitted to the TCM.

Install a diode, P/N 12112422, across the coil. It is important that the striped end of the diode be connected to the positive terminal of the coil and the other end of the diode be connected to ground.

Important: Be sure to insulate the diode with heat shrink tubing before installing as shown in the picture above.

Notice: Some relays (solenoids) may only have a positive post and will get their ground through their mounting bracket. In this case, the striped end of the diode is to be connected to the positive terminal and other end should be connected to the relay's (solenoid's) ground.

This repair will not be covered under warranty due to failure being caused by an aftermarket accessory.