6 Signs of a Bad Fuel Pump Relay (And Replacement Cost)

A failing fuel pump relay can turn a reliable vehicle into an unpredictable headache. This small electronic switch controls when your fuel pump receives power, making it a critical component for keeping your engine running.

Relay problems are often frustrating to correctly diagnose since the symptoms often resemble others and may seem random. Fortunately, the actual fix is relatively simple and inexpensive. Here are common symptoms of a bad fuel pump relay.

What’s a Fuel Pump Relay?

A fuel pump relay is an electrical switch that manages power delivery to your car’s fuel pump.

Rather than having the fuel pump constantly running or connecting it directly to a switch in the cabin, the relay acts as a middleman that can handle the high electrical current needed by the fuel pump while being controlled by low-current switches like your ignition.

fuel pump relay fuse box

Location

Most vehicles have their fuel pump relay in one of two locations. You’ll typically find it in the main fuse box under the hood, which is often near the battery or along one of the fender wells.

Some manufacturers place it inside the car, usually in the under dash fuse panel on the driver’s side. Check your owner’s manual for the exact location for your vehicle.

How It Works

When you turn your key to the “on” position or press your push-button start, the car’s computer sends a small electrical signal to the relay. This signal activates an electromagnet inside the relay, which pulls a set of heavy-duty electrical contacts together. These contacts complete the circuit and send power to the fuel pump.

If any part of this relay system fails (whether it’s the electromagnet, the contacts, or the wiring), your fuel pump won’t receive the power it needs. This interruption can cause various problems while starting or driving your vehicle.

Symptoms of a Bad Fuel Pump Relay

trouble starting car

1) Car Won’t Start

The most common sign of a failed fuel pump relay is a car that refuses to start, even though the engine cranks when you turn the key. Since the relay isn’t providing power to the fuel pump, no fuel gets delivered to the engine. You’ll likely hear the starter motor turning the engine over normally, but the engine won’t catch and run.

One of the best indicators of a fuel pump relay malfunction is if your car starts fine sometimes but fails to start at other times. In these cases, the relay may work intermittently due to internal electrical damage or heat-related issues.

2) Engine Stalls While Driving

Another common symptom is an engine that suddenly stalls while driving. This happens when the relay fails during operation, cutting power to the fuel pump. The engine will shut off all of a sudden, similar to if you were to run out of gas.

Obviously, this situation can be dangerous, especially if it occurs at highway speeds, heavy traffic, or not-so-good area. If this happens, your power steering and power brakes will still work long enough for you to safely pull over, but they’ll become much harder to use once the engine stops completely.

A failed relay can sometimes partially recover on its own after cooling down, which means your car might start again after sitting for a while. However, this is a temporary fix (and often just pure luck). If your relay has failed once while driving, it’ll likely happen again.

3) Long Crank Time Before Starting

car won't start

If your fuel pump relay is starting to fail but hasn’t completely given out, you might notice the engine takes longer to start than usual. This happens because the relay has a poor electrical connection, delivering inconsistent power to the fuel pump.

During these extended crank times, the starter motor runs normally, but the engine struggles to fire up because it’s not getting enough fuel. Once the engine does start, it usually runs fine. However, this cranking time can gradually get longer over several weeks or months as the relay continues to deteriorate.

4) No Fuel Pump Noise When Key Turned

In a properly working car, turning the key to the “on” position (without starting the engine) triggers a brief buzzing or whirring sound from the fuel pump. This noise usually lasts 2-3 seconds as the pump pressurizes the fuel system.

If the relay has failed, you simply won’t hear this noise. You can test this by having someone listen near the gas tank while you turn the key. Keep in mind that some newer vehicles are well-insulated, making this sound harder to hear. It’s often easier to hear the pump running if you remove the gas cap first.

While the absence of this noise isn’t a guaranteed sign of relay failure (it could also be a bad fuel pump or other electrical issue), it’s a helpful diagnostic clue when combined with other symptoms.

5) Intermittent Starting Issues

Unlike a complete failure where the car won’t start at all, a failing relay might work fine sometimes. Often, you may notice starting problems that seem to follow a pattern, like when it’s hot outside, or after the car has been running for a while.

These temperature-related patterns are common with failing relays since heat can affect their internal components. Sometimes letting the car sit for an hour or two allows the relay to cool down and work again temporarily.

6) Fuel Pump Continuously Running

In some cases, a failing relay can stick in the “on” position, causing the fuel pump to run ALL THE TIME, even when the car is turned off. You might notice a humming sound from the back of the car after you’ve removed the key.

A continuously running fuel pump is more than just an annoyance. Not only can it quickly drain your battery, it can also damage the fuel pump from excessive use.

Replacement Cost

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relay replacement cost

A fuel pump relay is typically an inexpensive part that ranges from $20 to $50 at most auto parts stores. Some luxury or high-end vehicles may have more expensive relays that cost up to $100, but this isn’t common.

Replacing a fuel pump relay is usually a very DIY-friendly job that only takes a few minutes. The hardest part is often identifying which relay controls the fuel pump, but usually there’s a diagram on the inside of the fuse box cover or printed in your vehicle’s owner’s manual.

If you choose to have a professional handle the replacement, expect to pay at least another $50 for their time. Though it may only take them five minutes to replace it, they won’t bill you in 5-minute increments.

Keep in mind that diagnostic time could add to the total cost if the mechanic needs to verify that the relay is actually the problem. Many shops charge one hour of diagnostic time ($80-120) before beginning repairs.

For comparison, this repair is much cheaper than replacing a fuel pump, which often costs $500-1000 or more. That’s why it’s always a good idea to test the relay first if you’re having fuel system issues.

How to Diagnose and Test a Fuel Pump Relay

Before replacing your fuel pump relay, it’s worth doing some basic diagnostic tests to confirm it’s actually the problem. Here’s a step-by-step process that can help you identify a bad relay.

Step #1: Listen for the Pump

Turn your key to the “on” position without starting the engine. You should hear a brief whirring sound (about 2-3 seconds) from near your gas tank. No sound could indicate a bad relay, but you’ll need to do more tests to be sure.

Step #2: Locate the Relay

Find your fuel pump relay in the fuse box. Check your owner’s manual or look for a diagram under the fuse box cover. The relay should look similar to other relays and will often be labeled “fuel pump” or “FP.”

Step #3: Check for Power

With the key in the “on” position, use a test light or multimeter to check if power is reaching the relay. Connect your test light to a good ground and probe the relay’s power input terminal. If there’s no power, the problem likely lies elsewhere in the electrical system.

Step #4: Swap with an Identical Relay

fuel pump relay

Many relays in your fuse box are identical. Find another relay that matches your fuel pump relay (like the A/C or horn relay) and swap them. If your car starts and runs with the swapped relay, your original relay is bad. Just remember to switch them back if the other relay controls something important like your brake lights.

Step #5: Test the Relay With a Multimeter

Remove the relay and set your multimeter to the resistance (ohm) setting. Test between the appropriate pins. You should get a reading around 70-120 ohms on the coil pins. The switch pins should show infinite resistance until the relay is energized. Your repair manual will show the exact pin layout and specifications.

Step #6: Inspect the Relay Socket

Remove the relay and check its socket for corrosion, bent pins, or loose connections. Clean the socket if needed and ensure all pins make good contact when the relay is installed.

If these tests suggest a bad relay, replacement is really your only option. Trying to repair a relay internally isn’t recommended since they’re sealed units and their low cost doesn’t make a repair attempt worth the time.

Step #6: Check for Heating Issues

If the car works when cold but fails after warming up, let the engine run until the problem occurs. Carefully spray the relay with electronics cleaner or compressed air. If the car starts working again temporarily, heat is likely causing the relay to fail.

Causes of Fuel Pump Relay Failure

fuse box

Like any electrical component, fuel pump relays can fail for several reasons. Understanding these causes can help you prevent premature failure and identify potential problems early.

  • Normal Wear and Tear: The most common cause of relay failure is simply age and use. The internal contacts inside the relay can wear down over time from thousands of on/off cycles. Most relays last 10-15 years under normal conditions, though some may fail sooner or last much longer.
  • Heat Damage: Relays are sensitive to extreme temperatures. Since many are located in the engine bay, they’re constantly exposed to heat cycles that can eventually damage their internal components. This is why relay problems often appear or worsen during hot weather or after the engine has been running for a while.
  • Moisture and Corrosion: If water gets into the fuse box or relay housing, it can corrode the relay’s electrical connections. This is more common in vehicles with known water leaks or those frequently exposed to wet conditions. Corroded connections can cause intermittent problems before complete failure occurs.
  • Electrical System Problems: Voltage spikes or other electrical system issues can damage a relay. If your car has other electrical problems, such as a failing alternator or bad battery, the irregular voltage can stress the relay and lead to premature failure.
  • Power Draw Issues: If your fuel pump draws more current than normal (which can happen as pumps age), it can overwork the relay and cause it to fail. This is similar to how a light switch might fail if you installed too powerful a light bulb.
  • Manufacturing Defects: Though less common, some relays can fail early due to manufacturing problems. This usually shows up fairly quickly after production, which is why these issues are often covered under warranty.
Kevin

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