* Neutral Safety Switch: This switch prevents the engine from starting unless the transmission is in Park (or Neutral, depending on the model year). If this switch is faulty, the engine might continue running even after you shift into Park and remove the key.
* Ignition Switch: A failing ignition switch might not properly disengage the power to the starter motor, even after you turn the key. This is less common but possible.
* Wiring Issues: A short circuit or damaged wiring in the ignition system could prevent the power from properly cutting off to the engine. This is a more difficult problem to diagnose and requires a skilled mechanic.
* Stuck Relay: Relays are electrical switches controlled by a low-voltage signal. A stuck relay in the ignition system could keep power flowing to the engine.
* Starter Motor Problems: While usually associated with starting issues, a faulty starter motor could sometimes cause the engine to remain running unexpectedly. This is less likely but possible.
* Computer Issues (PCM/ECM): In more modern vehicles, the Powertrain Control Module (PCM) or Engine Control Module (ECM) manages various engine functions. A malfunctioning PCM could prevent the engine from shutting off. This would require diagnostic tools to check for trouble codes.
* Aftermarket Accessories: Improperly installed aftermarket accessories could interfere with the vehicle's electrical system and cause the engine to stay on.
What to do:
1. Check the simplest things first: Make absolutely sure the transmission is in Park (or Neutral if appropriate). Try turning the key to the "off" position multiple times.
2. Listen carefully: Are there any unusual sounds coming from the engine compartment, like clicking relays or buzzing wires?
3. Have it professionally diagnosed: If the problem persists, take your Expedition to a qualified mechanic or Ford dealership. They have the diagnostic tools to identify the specific cause of the problem, and they're much better equipped to deal with potential wiring issues.
Don't continue driving the vehicle if it won't shut off reliably. This is a serious safety hazard.
