Fuel Pump Relay Autozone: Your Complete Guide to Replacement and Troubleshooting

Replacing a fuel pump relay found at Autozone is a straightforward repair that can save you significant money and get your car running again when you experience no-start or poor running issues related to the fuel pump. Autozone offers a wide selection of fuel pump relays compatible with virtually every make and model on the road, often at competitive prices, along with essential diagnostic and installation resources.

Understanding the Fuel Pump Relay's Critical Role

Your vehicle's fuel pump relay acts as an electrical switch controlled by the engine computer. When you turn the ignition key to the "On" position, the engine computer sends a small electrical signal to the relay. This signal triggers the relay to close its internal contacts, allowing significant electrical current to flow directly from the battery to the fuel pump. This powers the pump, enabling it to build the high pressure needed to deliver fuel to the engine. Without a functioning relay, the fuel pump gets no power, meaning no fuel reaches the engine, resulting in a failure to start. The relay also protects the engine computer from handling the high current required by the fuel pump.

Recognizing Symptoms of a Failing Fuel Pump Relay

A bad fuel pump relay is a common cause of no-start conditions and unreliable performance. Key symptoms include:

  1. Car Won't Start: This is the most frequent sign. You turn the key, the engine cranks (the starter motor turns the engine over), but the engine never actually starts and runs. You won't hear the fuel pump prime when you first turn the key to "On".
  2. Engine Stalls Intermittently: A relay failing while driving can cause the fuel pump to lose power abruptly. This results in the engine shutting off suddenly without warning while in motion. It might restart immediately or after sitting for a while.
  3. No Sound from the Fuel Pump: When you first turn the ignition key to the "On" position (before cranking), you should typically hear a faint humming or buzzing sound from the rear of the car (where the fuel tank is) for a couple of seconds. This is the fuel pump priming the system. No sound is a strong indicator of a power issue, often related to the relay or fuse.
  4. Unreliable Starting: The car starts normally sometimes but fails to start at other times, especially when hot or after short trips.
  5. Check Engine Light: While not always present, a failing relay can sometimes trigger fault codes related to fuel pressure or fuel pump circuits.

Differentiating Relay Failure from Fuel Pump Failure

Diagnosing the exact problem is crucial. Relay failure and fuel pump failure share the common symptom of the engine cranking but not starting. However, relays are generally cheaper and easier to replace. Before condemning the fuel pump, it's essential to check the relay and related fuses:

  • Relay Check: Test the relay (methods explained below) or try swapping it with an identical, known-good relay from another location in the fuse box (like the horn or A/C relay).
  • Fuse Check: Locate the fuel pump fuse (consult the owner's manual or fuse box lid diagram) and visually inspect it. Use a multimeter or test light to verify power on both sides of the fuse when the ignition is turned on.
  • Fuel Pump Power Test: If possible, verify power directly at the fuel pump's electrical connector while an assistant turns the ignition to "On." Requires wiring diagrams and careful probing.

Locating the Fuel Pump Relay

The fuel pump relay resides inside your vehicle's primary fuse box. Common locations include:

  • Engine Compartment: Often near the battery or against the firewall (the wall between the engine and passenger compartment).
  • Under the Dashboard: Often found near where the steering column meets the dash, on either the driver or passenger side.
  • Inside the Cabin: Occasionally found within or under the glove compartment or near the kick panels.

Consult these resources to find it reliably:

  1. Vehicle Owner's Manual: Always check here first. It contains specific diagrams for fuse and relay box locations and layouts.
  2. Fuse Box Lid Diagram: The plastic cover over the fuse box typically has a detailed diagram indicating the position and function of each fuse and relay.
  3. AutoZone Resources: Autozone offers online repair guides specific to your vehicle's year, make, and model. These guides often include fuse box layouts and relay locations.

Choosing the Correct Replacement Relay at Autozone

Autozone carries fuel pump relays for nearly every vehicle. To ensure you get the right part:

  1. Know Your Vehicle: Have your vehicle's year, make, model, and engine size ready.
  2. Find the Old Part: Remove the suspected faulty relay. Most relays have part numbers printed on the top or side casing. Use these numbers to cross-reference.
  3. Use AutoZone's Lookup Tools:
    • Store Counter: Provide your vehicle information or bring the old relay to any AutoZone counter. Staff can look up the correct part number.
    • Online Catalog: Enter your vehicle details into the AutoZone website search function to see compatible relays.

Common Relay Types and Features:

  • Standard Mini Relays: Very common shape with four or five pins.
  • Micro Relays: Smaller versions found in many modern vehicles.
  • ISO Relays: Follow a standardized size and pin layout.
  • Mounting: Ensure the new relay has the correct mounting style to fit securely in the socket in your fuse box.
  • Pins: Match the number of pins on the old relay. Five-pin relays are very common for fuel pumps. Check the terminal layout aligns.

AutoZone typically stocks reliable brands like Duralast. While choosing between standard and premium options may depend on your budget, both are quality replacements for this critical component.

How to Test a Fuel Pump Relay

Testing a suspect relay is relatively simple with basic tools:

Method 1: Shake Test (Preliminary)
* With the car off, remove the relay.
* Shake it gently. If you hear anything loose rattling inside (like broken parts), it's likely defective.

Method 2: Listen Test (In-Vehicle)
* With the relay plugged in and the ignition off, have an assistant turn the key to "On" (do not crank).
* Place your fingers on the relay. You should feel and hear a distinct "click" inside the relay as it energizes to prime the pump. No click suggests the relay is not engaging.

Method 3: Power and Coil Resistance Test (Out-of-Vehicle - Requires Multimeter)
Identify Terminals: Relay terminals are usually labeled on the relay casing or in diagrams. Common labels:
* 85 & 86: Coil Terminals (control circuit)
* 30: Power Input (from battery, via fuse)
* 87: Power Output (to fuel pump)
* 87a: Only in 5-pin relays, normally closed contact (often unused for fuel pump). 4-pin relays omit this.
Test the Coil:
1. Set your multimeter to Ohms (Ω).
2. Place probes on terminals 85 and 86. A good coil shows moderate resistance (typically between 50-150 ohms). Open circuit (infinite resistance) = bad coil. Zero ohms = shorted coil.
Test the Contacts:
1. Set multimeter to Continuity (beep) or low Ohms.
2. Test between terminals 30 and 87a (if present). There should be continuity when the relay is de-energized (normal state). No continuity = bad contacts.
3. No continuity should exist between 30 and 87 in the de-energized state.
4. Testing Closure: To test between terminals 30 and 87, you need to energize the coil. Apply 12 volts across terminals 85 (+) and 86 (-). A 9V battery or power supply works, or use jumper wires carefully from your car battery (tape exposed leads except at connection points). WARNING: Be cautious - avoid sparks and short circuits. When energized:
* Continuity should exist between terminals 30 and 87.
* Continuity between 30 and 87a (if present) should disappear. If the relay fails any of these steps, replace it.

How to Replace the Fuel Pump Relay

Replacement is usually very simple:

  1. Locate: Identify the fuel pump relay location using your owner's manual or fuse box diagram.
  2. Access: Open the fuse box cover.
  3. Identify: Double-check you have the right relay. Match its position to the diagram on the fuse box lid.
  4. Remove: Firmly grasp the relay and pull it straight out of its socket. Do not twist or rock it excessively.
  5. Compare: Inspect the old relay and the new Autozone replacement relay. Ensure the shape, number of pins, and pin pattern match exactly.
  6. Install: Align the pins on the new relay perfectly with the sockets. Press the relay firmly and evenly straight down into the socket until it is fully seated.
  7. Test: Turn the ignition key to "On." You should now hear the fuel pump prime for a couple of seconds. Attempt to start the engine.
  8. Reassemble: Replace the fuse box cover.

AutoZone's Advantages for Your Fuel Pump Relay Needs

Choosing AutoZone for your fuel pump relay purchase offers several benefits:

  • Extensive Selection: They stock relays compatible with nearly all vehicles, both domestic and import.
  • Local Availability: Likely have the relay you need in stock at a nearby store for immediate purchase.
  • Competitive Pricing: Relays are generally affordable, and AutoZone provides good value.
  • Expert Advice: Counter staff can help locate the relay in your car and ensure you get the correct part.
  • Loan-A-Tool Program: Need a multimeter to test? AutoZone often loans tools for free with a deposit.
  • Convenient Returns: Simple return process if the part is incorrect or defective.
  • Online Resources: Access repair guides, fuse box diagrams, and vehicle-specific information via their website.
  • Warranty: Duralast relays typically come with a limited warranty.

Troubleshooting After Relay Replacement

If replacing the fuel pump relay doesn't solve the problem, further investigation is needed:

  1. Verify Correct Relay: Re-confirm you purchased and installed the exact replacement part number.
  2. Check Related Fuses Again: Re-inspect the main fuel pump fuse. Also, check other critical fuses (e.g., ECM/PCM fuse, ignition fuse) as their failure can prevent the relay from receiving the signal to turn on.
  3. Confirm Fuel Pump Operation:
    • Listen for the pump priming sound at ignition "On".
    • Perform a fuel pressure test using a gauge connected to the Schrader valve on the fuel rail (if equipped).
    • Check for power and ground directly at the fuel pump's electrical connector with ignition "On" (requires wiring diagrams and safe probing).
  4. Inspect Wiring: Look for damaged, corroded, or loose wiring connections at the fuse box, relay socket, or fuel pump. Check ground points for corrosion.
  5. Consider Other Causes: While the relay is a common failure point, consider:
    • A completely failed fuel pump.
    • A faulty fuel pump driver module (some vehicles).
    • A failed crankshaft position sensor (prevent spark and injector pulse).
    • A security system lockout.
    • A major failure within the engine computer (ECM/PCM).

When Professional Help is Advised

While replacing a fuel pump relay at AutoZone is usually a DIY repair, seek professional assistance if:

  • You are uncomfortable with electrical diagnosis or testing.
  • You cannot locate the relay using the manual or diagrams.
  • Replacing the relay doesn't fix the problem and you cannot perform further diagnostics.
  • The problem involves complex wiring issues or requires advanced equipment.
  • Your vehicle lacks obvious relay access or requires component removal.

A Cost-Effective Repair Path

Finding the correct fuel pump relay at Autozone provides a fast, economical solution to a common automotive problem that can cause significant inconvenience. Their combination of parts availability, knowledgeable staff, repair resources, and competitive pricing makes them a practical choice. Accurately diagnosing the relay failure as the root cause saves unnecessary expense and effort, especially against misdiagnosing a failed fuel pump. Keeping this vital electrical component working ensures fuel delivery every time you start your engine.

Back to blog