1. Fuel Pump Relay: This is the most common cause. The relay acts as a switch, activating the fuel pump only when the ignition is on. A faulty relay might stick closed, keeping power to the pump even when the key is off.
* How to check: Locate the fuel pump relay (consult your owner's manual or a reliable online resource for its location; often in the underhood fuse box). Visually inspect it for any damage. You can swap it with another relay of the same amperage (if you have a spare) to see if the problem follows the relay. If you swap it and the problem goes away, you've found your culprit.
2. Ignition Switch: The ignition switch might be malfunctioning, failing to properly interrupt the power supply to the fuel pump circuit.
* How to check (advanced): This requires more advanced electrical testing. You'll need a multimeter to check for continuity and voltage at the ignition switch terminals. Refer to a wiring diagram to identify the correct wires and their function.
3. Wiring Issues: A short circuit in the wiring harness leading to the fuel pump could provide a constant power source. This could be caused by damaged insulation, corroded connections, or a wire rubbing against a grounded component.
* How to check: Visually inspect the wiring harness leading from the fuel pump relay to the fuel pump. Look for any signs of damage, fraying, or corrosion. This requires carefully tracing the wires.
4. PCM (Powertrain Control Module): While less likely, a faulty PCM could be sending the wrong signals to the fuel pump relay. This is usually diagnosed with a scan tool capable of reading diagnostic trouble codes (DTCs).
* How to check: You'll need a scan tool to check for any relevant codes. This is best left to a professional mechanic as incorrect PCM diagnosis can lead to more issues.
5. Fuel Pump Inertia Switch: Some vehicles have an inertia switch (a safety feature that cuts power to the fuel pump in a collision) that might be stuck in the 'off' position, preventing the pump from switching off properly. Try resetting it (usually involves pushing a button or flipping a switch). This is less likely to cause the pump to *stay* on, however.
Important Safety Precautions:
* Disconnect the battery negative terminal before starting any electrical work to prevent injury.
* Fuel is flammable: Be careful when working around the fuel system.
* Don't start the engine while troubleshooting.
Recommendation:
If you're not comfortable working with car electrical systems, it's best to take your S10 to a qualified mechanic. A continuous running fuel pump can drain your battery and potentially be a fire hazard. The relay is the easiest and cheapest place to start, but a proper diagnosis may require specialized tools and expertise.
