Here's how to test a fuel pump relay, noting that the specific steps may vary slightly depending on your vehicle's make and model:
1. Locate the Fuel Pump Relay:
* Consult your vehicle's repair manual: This is the best resource for the exact location of the fuel pump relay. It will likely be in the under-hood fuse box, but could also be in the interior fuse box or even under the dashboard. The manual will also show you a diagram of the fuse box.
* Look for a diagram on the fuse box cover: Many fuse boxes have diagrams indicating the location of relays and fuses. The fuel pump relay is usually labeled.
* Online resources: Search online for your vehicle's year, make, and model, along with "fuel pump relay location." Many forums and websites have this information.
2. Gather Your Tools:
* Test light or multimeter: A multimeter is more precise, but a test light will suffice for basic testing.
* Wire diagram (optional but highly recommended): This will help you identify the correct terminals on the relay.
3. Visual Inspection:
* Check for any obvious damage: Look for signs of burning, corrosion, or physical damage to the relay. Replace a visibly damaged relay.
4. Testing with a Multimeter (Preferred Method):
* Disconnect the relay: Carefully remove the relay from its socket.
* Identify the terminals: Relays usually have 4 or 5 terminals. A wire diagram is crucial here. Common terminals are 85, 86, 30, and 87 (sometimes 87a). They may be numbered differently on your relay.
* Check for continuity (Resistance):
* Between terminals 30 and 87 (or 87a): With the multimeter set to ohms (Ω), check for continuity (a low resistance reading, close to 0) between these terminals. If there is no continuity, the relay is faulty.
* Between terminals 85 and 86: There should be continuity between these terminals as well. Lack of continuity suggests an internal fault.
* Check for power:
* With the ignition ON: Set your multimeter to volts (V) DC. Probe one lead to a good ground (bare metal on the engine block is a good choice) and the other lead to terminal 30. You should have battery voltage (12V). If not, there may be a problem with the power supply to the relay.
* With the ignition ON: Test for power at terminal 85. You should have power with the key in the ON position.
5. Testing with a Test Light:
* Similar to the multimeter test, but less precise: Connect one lead of the test light to a good ground. Then, test for power at terminal 30 (ignition ON) and then at terminal 85 (ignition ON). The test light should illuminate if power is present. Continuity testing is harder with a test light and often requires jumping pins to test internally. This is why a multimeter is preferred.
Interpreting the Results:
* If the relay fails any of these tests (lack of continuity or no power where expected): Replace the relay. It's a relatively inexpensive part, and replacing it is much easier than diagnosing more complex issues.
* If all tests pass but the fuel pump still doesn't work: The problem likely lies elsewhere in the fuel system (fuel pump itself, wiring, etc.). Further diagnostic steps are needed.
Important Considerations:
* Always disconnect the negative battery terminal before working on any electrical components.
* If you're not comfortable performing these tests, take your vehicle to a qualified mechanic. Incorrectly diagnosing a fuel system problem could be dangerous.
* Double-check all connections before applying power.
This guide provides a general approach. Refer to your vehicle's specific repair manual for accurate details and diagrams related to your fuel pump relay.
