* Faulty Fuel Pump Relay: This is the most common culprit. The relay acts as a switch, activating the fuel pump only when the ignition is on. A stuck relay will keep the pump energized even after the key is removed. This relay might be failing to open its contacts.
* Short Circuit in the Wiring: A short circuit in the wiring leading to the fuel pump can create a continuous power path, bypassing the relay and keeping the pump running. This could be anywhere from the relay to the pump itself, potentially even within the wiring harness. Inspect the wiring carefully for damage or frayed insulation.
* Faulty Ignition Switch: While less likely, a malfunctioning ignition switch might not be properly breaking the circuit to the fuel pump, even after the key is turned off.
* Problem with the Pump's Inertia Switch (sometimes called the Crash Switch): This switch is a safety device designed to cut off the fuel pump in a collision. If it's malfunctioning and stuck in the "on" position, it could keep the pump running. It's usually located under the dash or near the fuel tank.
* PCM (Powertrain Control Module) Issue (Less Likely): Though less probable, a faulty PCM could be sending an incorrect signal to the fuel pump, even when the ignition is off. This is less likely because other engine systems would likely also be malfunctioning.
Immediate Action:
* Disconnect the Negative Battery Cable: This is the most important step to prevent further damage to the fuel pump (it can overheat and burn out) or a potential fire hazard. Do this immediately.
Troubleshooting Steps:
1. Check the Fuel Pump Relay: Locate the relay (usually in the under-hood fuse box or a separate relay center). Visually inspect it for any signs of damage. Try swapping it with a known good relay of the same type (be sure to note its location before swapping). If the problem goes away, you've found the culprit.
2. Inspect the Wiring: Carefully examine the wiring harness from the relay to the fuel pump for any signs of damage, fraying, or shorts. Look for any areas where wires might be touching metal or each other.
3. Check the Inertia Switch: Locate the inertia switch and test it according to your vehicle's service manual. If it's resettable, reset it.
4. Test the Ignition Switch (Advanced): This requires more advanced electrical testing equipment and knowledge. It's best left to a qualified mechanic unless you are experienced with automotive electrical systems.
Leaving the fuel pump running for an extended period will severely damage it and could lead to a fire. Address this issue immediately. If you're not comfortable troubleshooting electrical systems, take your S10 to a qualified mechanic.
