Here's how to test the fuel pump relay:
1. Locate the Fuel Pump Relay:
* Consult your owner's manual or a reliable online repair manual (like Chilton or Haynes) to find the location of the fuel pump relay. It's usually in the underhood fuse box (power distribution center), but could be elsewhere. The manual will show you a diagram of the fuse box layout. The relay itself will likely be labeled (though sometimes not clearly).
2. Gather Your Tools:
* Test light: A simple test light with a pointed probe is ideal.
* Multimeter (optional but recommended): A multimeter provides more precise readings of voltage and continuity.
* Wire diagram (highly recommended): A wiring diagram will show you which terminals on the relay should have power, ground, and connection to the fuel pump.
3. Safety Precautions:
* Disconnect the negative battery cable before starting any testing. This prevents accidental shorts and protects the vehicle's electrical system.
4. Testing Procedure (Using a Test Light):
* Identify the relay's terminals: Relays typically have four terminals. You'll need to identify which terminals are for power in, power out (to the fuel pump), ground, and the coil (the electrically activated switch inside the relay). Your wiring diagram is crucial here.
* Check for power at the power input terminal: Turn the ignition key to the "ON" position (don't crank the engine). Use the test light to check for power at the input terminal of the relay. One side of the test light connects to a good ground, the other probes the relay terminal. If the light doesn't illuminate, there's a problem with the power supply to the relay, not necessarily the relay itself.
* Check for power at the output terminal: With the ignition still on, check for power at the output terminal of the relay that leads to the fuel pump. If there is power, the relay is likely working, and the problem may be elsewhere (e.g., a blown fuse, wiring fault, bad fuel pump). If no power, the relay may be faulty.
* Check for ground: Confirm a good ground connection to the relay's ground terminal.
5. Testing Procedure (Using a Multimeter):
* Continuity test (Coil): With the relay removed from the socket, set your multimeter to the continuity test (usually a diode or a bell symbol). Test the continuity between the coil terminals. If the multimeter beeps or shows a low resistance, the coil is good. If not, the coil is likely open and the relay is bad.
* Voltage test: With the relay in its socket and the ignition on, measure the voltage at the relay's input terminal. You should have battery voltage (around 12V). Then, check the voltage at the output terminal. If you have voltage at the input but not the output with the key on, the relay is likely bad.
Important Considerations:
* Multiple relays: Some systems use multiple relays, one as a primary switch and another as a safety shut-off. You need to identify which relay is for the fuel pump.
* Fuse: Check the fuse(s) associated with the fuel pump circuit *before* testing the relay. A blown fuse is a much more common problem.
* Fuel pump itself: If the relay tests good, the fuel pump itself could be faulty. This requires a different testing method involving measuring fuel pump pressure.
If after these tests you still suspect a faulty relay, replace it with a new one of the correct specifications. Again, if you are uncomfortable performing these tests, take your vehicle to a qualified mechanic.
