How to Check a Fuel Pump Relay Switch

Internal components of an electro-mechanical relay

If you are having trouble with the fuel system in your vehicle and you suspect the fuel pump relay, here is an easy way to determine whether the relay is working as it should or you need to replace it. You need a minimum understanding of electrical circuits, but if you want to learn basic troubleshooting procedures, this is a good place to start. This guide applies to electro-mechanical relays.

Things You'll Need

• Ohmmeter Fused jumper wire Regular jumper wire

Instructions

1. Park your car on a level surface and locate the fuel pump relay. In some models, this relay is located in the fuse box or next to it, inside the engine compartment, toward the firewall. Some vehicle models have the fuel pump relay installed underneath the dashboard. Once you locate the relay, remove it, being careful not to break the plastic lock tabs.

2. Locate the two control circuit terminals and the two power circuit terminals on your relay. Most relays come with a small schematic on the case itself identifying these terminals. Otherwise, look at the wires connected at the mounting base of the relay. Usually, the two thick wires connect to the power terminals and the two thin wires to the control terminals.

3. Check for continuity at the power terminals. Using an ohmmeter, set the unit to its lowest resistance range. Touch the meter leads to the power terminals on the relay. If you read zero resistance or a resistance value in the hundredths or thousandths, replace the relay. If you read infinite resistance, go on to the next step.

4. Connect one end of a fused jumper wire to one of the relay control terminals and the other end of the jumper wire to the positive terminal of the car battery. Connect a regular jumper wire to the other control terminal and the other end of the jumper wire to a good ground on your car. As you touch the jumper wire to ground, you should hear a click coming from the relay. If you do not hear the click sound, replace the relay.

5. Leave the jumper wires connected to the pump relay and check for continuity at the relay power terminals as you did in Step 3. This time, you should get a resistance value. If you receive infinite resistance--no reading at all--the relay contact points might be burned. Replace the relay.

Tips & Warnings

• If you need help locating the fuel pump relay on your car, consult your car owner's manual or vehicle service manual. You can buy one at most auto parts stores or consult one for free at your local public library.