* Blown Fuse: The most common cause. Check the fuse specifically designated for the fuel pump circuit in your vehicle's fuse box (often under the hood or in the passenger compartment). A blown fuse will look visibly damaged (blown or melted).
* Faulty Fuel Pump Relay: While you mentioned it's good, a relay can appear good but still fail intermittently or under load. Testing it with a multimeter to ensure proper switching is the best way to diagnose this. A simple visual inspection isn't sufficient.
* Wiring Issues: A break, short, or corrosion in the wiring between the relay, the fuel pump, the PCM (Powertrain Control Module), or the power source can interrupt the circuit. This requires careful inspection of the wiring harness.
* PCM (Powertrain Control Module) Problem: The PCM controls the fuel pump relay. A malfunctioning PCM can prevent it from sending the signal to energize the relay. This is a more complex issue requiring diagnostic tools.
* Ignition Switch Malfunction: The fuel pump relay usually only gets power when the ignition is turned on. A problem with the ignition switch can prevent power from reaching the relay.
* Safety Interlock Switch Problem: Certain safety features (like a tilt sensor in a rollover situation) can cut power to the fuel pump. If this is malfunctioning, it might be unintentionally cutting the power.
* Incorrect Wiring: Although less likely, it's possible there was a wiring error during maintenance or repair.
Troubleshooting Steps:
1. Check the Fuse: This is the easiest and first step.
2. Test the Fuel Pump Relay: Use a multimeter to verify it's functioning correctly. Many online resources explain how to test relays.
3. Inspect Wiring: Visually inspect the wiring harness for any damage, corrosion, or loose connections, especially near the relay and fuel pump.
4. Consult a Wiring Diagram: A wiring diagram specific to your vehicle's year, make, and model will show the fuel pump circuit and help you trace the problem.
5. Use a Diagnostic Scanner (OBD-II): This can help identify any trouble codes related to the fuel pump or PCM.
If you're not comfortable working with car electronics, it's best to take your vehicle to a qualified mechanic for diagnosis and repair. Attempting repairs without proper knowledge can be dangerous.
