Troubleshooting 101: How to Test My Fuel Pump Relay and Save Money

If your car is struggling to start or dies unexpectedly, a faulty fuel pump relay could be the culprit. The fuel pump relay acts as a switch, controlling the flow of electricity to the fuel pump, which in turn delivers fuel to your engine. Knowing how to test your fuel pump relay is a valuable skill for any car owner, as it can save you time and money by helping you diagnose the problem before seeking professional help. This guide will walk you through the process of testing your fuel pump relay, equipping you with the knowledge to confidently troubleshoot this critical component.

Understanding the Fuel Pump Relay

Before diving into the testing process, let’s understand what the fuel pump relay does and why it’s so important.

The fuel pump relay is a small, electrical component that acts as an intermediary between the ignition system and the fuel pump. When you turn the key to the “on” position, the relay receives a signal from the ignition system. This signal activates the relay, allowing electricity to flow to the fuel pump, which then starts pumping fuel to the engine.

Here’s a simplified breakdown:

• Ignition Key: You turn the key to “on”.
• Ignition System: The ignition system sends a signal to the fuel pump relay.
• Fuel Pump Relay: The relay receives the signal and closes the circuit, allowing electricity to flow.
• Fuel Pump: The fuel pump receives electricity and starts pumping fuel.
• Engine: The engine receives fuel and starts.

Symptoms of a Faulty Fuel Pump Relay

Several symptoms can indicate a problem with your fuel pump relay. Recognizing these symptoms is the first step in diagnosing a potential relay issue.

• No Start: This is the most common symptom. If your car won’t start, a faulty relay could be preventing the fuel pump from receiving power.
• Intermittent Starting: If your car starts sometimes but not others, it could be a sign of a faulty relay that intermittently fails to activate the fuel pump.
• Engine Stalling: If your engine stalls while driving, a faulty relay could be causing the fuel pump to stop working, leading to a loss of fuel supply.
• Clicking Noise: You may hear a clicking sound coming from the relay box under the hood when you try to start the car. This noise could indicate a relay that is failing to engage properly.

Tools You’ll Need to Test Your Fuel Pump Relay

Before you begin testing, gather the necessary tools:

• Multimeter: This essential tool measures voltage, current, and resistance. You’ll need a multimeter with both DC voltage and resistance measurement capabilities.
• Test Light: A test light can be used to check for continuity in electrical circuits.
• Wire Diagram: A wiring diagram for your specific vehicle will help you identify the fuel pump relay location and its connections.
• Safety Glasses: Always protect your eyes when working with electrical components.

Locating the Fuel Pump Relay

The location of the fuel pump relay varies depending on the make and model of your vehicle. It’s usually located in the engine compartment’s fuse box or relay box. Consult your vehicle’s owner’s manual or a wiring diagram to find the exact location.

How to Test Your Fuel Pump Relay: A Step-by-Step Guide

Now, let’s get to the heart of the matter: testing the fuel pump relay. Follow these steps:

1. Disconnect the Battery: For safety, disconnect the negative terminal of your car battery before working on electrical components.
2. Locate the Relay: Using your vehicle’s manual or wiring diagram, find the fuel pump relay. It will usually be labeled with “FP” or “Fuel Pump“.
3. Remove the Relay: Carefully remove the fuel pump relay from its socket.
4. Visual Inspection: Examine the relay for any signs of damage, such as burn marks or corrosion. If you notice any damage, it’s likely the relay is faulty.
5. Continuity Test: Use your multimeter to test the continuity of the relay’s contacts. Set the multimeter to the resistance setting and touch the probes to the appropriate terminals.

• Terminal 30 and 87: This connection should show continuity when the relay is energized.
• Terminal 85 and 86: This connection should show continuity when the relay is not energized.
• Terminal 87a: This terminal is typically connected to the fuel pump.

6. Voltage Test: With the ignition key in the “on” position, use your multimeter to measure the voltage across terminals 85 and 86. You should get a voltage reading close to the battery voltage.
7. Test Light Method: If you don’t have a multimeter, you can use a test light to check for continuity. Connect the test light to the positive terminal of the battery and touch the other end to the fuel pump relay’s terminal 87a. With the ignition key in the “on” position, the test light should illuminate if the relay is working.

Interpreting the Results

• Continuity Test: If you don’t get a reading on the continuity test, the relay is likely faulty.
• Voltage Test: If you don’t get a voltage reading across terminals 85 and 86, there might be a problem with the ignition system or the wiring leading to the relay.
• Test Light: If the test light doesn’t illuminate, the relay is likely faulty.

Replacing the Fuel Pump Relay

If your testing reveals a faulty relay, you’ll need to replace it. Here’s how:

1. Purchase a new relay: Ensure you buy a relay specifically designed for your vehicle. You can find the correct relay at your local auto parts store or online.
2. Install the new relay: Carefully insert the new relay into the socket, ensuring it’s properly seated.
3. Reconnect the battery: Reconnect the battery’s negative terminal.
4. Test the new relay: Start the car and check that it runs smoothly. If the problem persists, there might be a different issue, and you should consult a mechanic.

Troubleshooting Beyond the Relay

While a faulty fuel pump relay is a common cause of starting problems, other issues can mimic similar symptoms. Here are some additional troubleshooting steps:

• Check the Fuel Pump: If the relay is working correctly, but the car still won’t start, the fuel pump itself might be faulty. You can test the fuel pump by listening for a humming sound when you turn the ignition key to the “on” position.
• Inspect the Fuel Pump Fuse: A blown fuse can also prevent the fuel pump from receiving power. Check the fuse box for a blown fuse related to the fuel pump.
• Examine the Fuel Lines: Check the fuel lines for leaks or blockages.

Time to Get Back on the Road

Knowing how to test your fuel pump relay can save you time, money, and frustration when dealing with starting problems. By following the steps outlined in this guide, you can confidently diagnose a faulty relay and get your car back on the road quickly. Remember, if you’re unsure about any of the steps or encounter difficulties, it’s best to seek professional help from a certified mechanic.

Common Questions and Answers

Q: How long does a fuel pump relay typically last?

A: The lifespan of a fuel pump relay can vary depending on factors like driving conditions, environmental factors, and the quality of the relay itself. However, a well-maintained relay can typically last for several years.

Q: Can I use a universal fuel pump relay?

A: While some universal relays might seem like a suitable replacement, it’s highly recommended to use a relay specifically designed for your vehicle. This ensures compatibility and proper functionality.

Q: Can I test the fuel pump relay without a multimeter?

A: While a multimeter is the most accurate way to test the relay, you can use a test light to check for continuity. However, a multimeter provides a more comprehensive assessment.

Q: What happens if the fuel pump relay is not working?

A: A faulty fuel pump relay will prevent the fuel pump from receiving power, causing the engine to not start or stall while driving.

Q: Can I drive my car if the fuel pump relay is faulty?

A: It’s not recommended to drive your car with a faulty fuel pump relay. This could lead to engine damage or even a dangerous situation if the car stalls while driving.