1998 Ford Explorer Fuel Pump Relay Location: Your Fast & Accurate Guide

The fuel pump relay in your 1998 Ford Explorer is located within the main Power Distribution Box (PDB), commonly called the underhood fuse box. This critical electrical component occupies position #21 inside that black box situated in the engine compartment.

If your Explorer cranks but won't start, experiences sputtering, or has no fuel pump noise when turning the key to "Run," locating and checking the fuel pump relay is often one of the fastest and most important diagnostic steps. Knowing exactly where it is saves precious time and frustration. Let’s get you straight to the source.

Pinpointing the 1998 Ford Explorer Fuel Pump Relay Location (Position #21)

  1. Open the Hood: Safely pull the hood release lever inside your Explorer and secure the hood in the fully open position using the prop rod.
  2. Locate the Main Power Distribution Box (PDB): This is a prominent, rectangular black plastic box usually situated on the driver's side (left side when facing the windshield) of the engine compartment. It's mounted towards the rear, near the firewall or the fender wall. This box houses most fuses and several important relays for your Explorer.
  3. Remove the PDB Cover:
    • The cover is secured by several plastic tabs or clips around its edges.
    • Carefully press down or slide these clips to release them. They may require slight upward pressure near the clip points after unlatching.
    • Gently lift the cover straight off. Avoid forcing it; if stuck, double-check for hidden clips. Set the cover aside in a safe place.
  4. Identify Relay Position #21:
    • Once the cover is off, you'll see an array of large fuses and smaller relays plugged into sockets.
    • Locate the diagram: Look inside the underside of the PDB cover you just removed. Ford typically molds or prints a detailed diagram showing the exact layout of the fuse and relay positions, along with their functions and amperage ratings. This is your most reliable guide. THE DIAGRAM IS YOUR KEY.
    • Position #21: Find the position clearly labeled as #21 on the diagram. It should also be explicitly labeled as the "Fuel Pump Relay," "FP Relay," or have a matching amperage/symbol description indicating the fuel system. Visually locate socket #21 within the PDB itself – the sockets are often numbered directly beside them on the PDB base.
  5. Recognize the Relay:
    • The fuel pump relay itself is a small (usually black or gray), cube-shaped component plugged into socket #21.
    • It will look essentially identical to the other nearby relays (like the EEC Power, Horn, PCM, or Fog Lamp relays).
    • Its identity is defined solely by its socket position (#21), not by its color or any markings on the relay body itself.

(Visual Guide Diagram Placeholder - Showing Underhood PDB Location and Relay #21 Position)

Why Knowing This Location Matters: Symptoms of Relay Failure

The fuel pump relay acts like a heavy-duty switch controlled by your Explorer's Powertrain Control Module (PCM). It allows a small electrical signal from the PCM to safely control the high current required by the fuel pump. When the relay fails or its contacts get dirty or corroded, several common problems emerge:

  • Engine Cranks But Won't Start: This is the most classic symptom. The starter motor turns the engine over, but without fuel being pumped, ignition can't happen.
  • No Fuel Pump Sound at Key-On: When you turn the ignition key to the "Run" position (without starting), you should hear a distinct humming or buzzing sound coming from the rear of the vehicle (near the fuel tank) for 2-3 seconds. This is the fuel pump priming the system. Complete silence at this point strongly suggests a fault with the relay, fuse, the pump itself, or the wiring/inertia switch. The relay is a top suspect.
  • Engine Sputtering or Stalling While Driving: Intermittent relay failure can cause the fuel pump to cut out unexpectedly, leading to hesitation, loss of power, or sudden stalling, sometimes restarting after cooling down briefly.
  • Intermittent No-Start Issues: A failing relay might work sometimes and not others, making diagnosis tricky. You might experience no-start problems that seem random or only occur after the vehicle has been sitting.

Accessing & Inspecting the Relay (Step-by-Step)

Once you've located Position #21:

  1. Power Off: Before touching anything, ensure the ignition is turned completely OFF. For maximum safety, consider disconnecting the negative (-) battery cable, though not always strictly necessary for a simple visual inspection or relay pull.
  2. Locate Relay #21: Visually confirm you've found the correct socket using the diagram and the socket number.
  3. Removing the Relay:
    • Relays are usually removed by pulling straight upwards with a steady, even force.
    • Grasp the relay firmly by its sides or top. Avoid pulling on any wires attached nearby.
    • Use your fingers; tools are rarely needed and can damage the socket. If stuck, gently wiggle side-to-side while pulling up.
    • Listen/feel for it unseating from its socket.
  4. Visual Inspection:
    • Exterior: Look for obvious damage: melted plastic, cracks, chips, or signs of overheating (browning or distortion).
    • Terminal Pins: Examine the metal pins protruding from the bottom of the relay. Look for:
      • Burns/Melting: Dark spots, deformation, or actual melting.
      • Corrosion: A green, white, or bluish crusty substance covering the metal.
      • Bent/Damaged Pins: Ensure pins are straight and undamaged.
    • Socket: Take a quick look inside socket #21. Check for corrosion, debris, or any signs of damage on the metal contacts inside the box. Burn marks or melted plastic in the socket itself are serious signs of electrical issues and require immediate attention.

Testing the Fuel Pump Relay (The Swap Test & The Shake Test)

While advanced testing involves using a multimeter or a power supply, there are two very effective and simple real-world tests you can perform immediately:

  1. The Swap Test (Best Method):

    • Identify another relay in the PDB that has the EXACT same part number and is the SAME PHYSICAL SIZE AND SHAPE as the one you pulled from position #21. Good, safe candidates are often the Horn Relay (typically position #18) or sometimes the A/C Compressor Clutch Relay (if equipped - check diagram).
    • Important: NEVER swap a relay with a different part number or pin configuration. You risk damaging other circuits.
    • Remove the Known Good Relay: Remove the identical relay from its socket.
    • Install the Known Good Relay: Take this confirmed working relay and plug it securely into the Fuel Pump Relay socket (#21).
    • Re-test: Turn the ignition key to "Run." Do you now hear the fuel pump prime? Does the engine start? If yes, your original fuel pump relay in #21 is likely bad.
    • Confirm: Plug the suspected bad relay into the donor socket (where you took the good relay from – e.g., the horn socket). Test the horn. If the horn doesn't work with the suspected bad relay in place (and the suspect relay is the correct one for that socket), that confirms the relay is faulty.

  2. The Shake Test (For Intermittent Faults):

    • With the original relay removed from socket #21 and ignition OFF, hold the relay firmly.
    • Shake it vigorously near your ear.
    • Listen: Do you hear anything rattling inside? A distinct "rattle" usually indicates that internal parts have broken off or that the relay is physically damaged internally. A rattling relay is almost certainly defective.
    • Note: A silent relay isn't necessarily good, but a rattling one is almost always bad.

Replacement Steps and Important Considerations

If testing confirms the relay is bad, replacing it is straightforward:

  1. Obtain the Correct Replacement Part:
    • Part Number is Crucial: The part number is usually printed on the relay casing itself (e.g., F57B-14B192-AA, F1SF-14B192-AA are common Ford types). This is the best way to identify it.
    • Use the Old Relay: Take the old relay to an auto parts store. Match it by part number AND appearance (pin count and layout).
    • Buy OEM Equivalent: Stick with reputable brands like Motorcraft (Ford's parts brand), Bosch, Standard Motor Products, or ACDelco. Avoid the cheapest, no-name relays for critical functions.
    • Confirm Location: Double-check the parts store provides a relay specifically listed for the Fuel Pump Relay position (#21) in a 1998 Ford Explorer.
  2. Installation:
    • Align the new relay correctly over socket #21. The relay body often has chamfered corners or keying tabs to ensure it only fits one way. The socket pins might also be offset. If it doesn't seat easily, don't force it! Rotate it 90 degrees or double-check orientation.
    • Press the relay firmly and evenly straight down into the socket until it clicks or seats completely. You should feel it engage.
  3. Test: Turn the ignition key to "Run" and listen for the fuel pump priming hum for 2-3 seconds. Attempt to start the engine.
  4. Replace the PDB Cover: Once confirmed working, snap the cover securely back onto the Power Distribution Box, ensuring all clips latch properly to protect the components inside.

Critical Considerations:

  • Fuse FIRST: Always check the Fuel Pump Fuse (commonly 20A) BEFORE blaming the relay or replacing it. The fuse is also in the PDB – check your diagram (often labeled "FP," "Fuel Pump," "PCM," "Engine," or position #1). A blown fuse will cause identical symptoms to a failed relay and is simpler/cheaper to fix. Replace a blown fuse only with one of the exact same amperage rating.
  • Inertia Switch: The 1998 Explorer has an inertia safety switch (fuel pump cut-off switch), usually located on the front passenger-side floor area (kicker panel near the firewall or under the dash). If your Explorer has experienced an impact (even a big pothole), this switch might have tripped, cutting power to the fuel pump. It has a prominent red button on top – press it firmly to reset it. Always check this immediately after a no-start incident, especially one following a bump. It's designed as a safety feature to prevent fuel flow after a collision.
  • Electrical Issues: While relay failure is common, persistent problems after relay replacement (fuses blowing, relays burning out quickly) point to more serious issues like a short circuit in the pump wiring, a failing pump drawing excessive current, or problems in the PDB. Professional diagnosis is essential if problems recur. Do not ignore repeated fuse or relay failures.
  • Pump Failure: Even with a good relay and fuse, the mechanical fuel pump itself can fail. If you hear the pump running at key-on but the engine still won't start, fuel pressure testing becomes necessary.
  • Handling Electronics: Handle the relay by its body, not its pins, to avoid oils from your skin causing corrosion. Ensure hands are reasonably clean and dry. Avoid installing relays with wet hands or during rain.
  • Securing the Cover: Leaving the PDB cover off exposes critical electrical components to moisture and dirt. Always reinstall it after any fuse or relay work.

Beyond the Relay: Related System Checks

Diagnosing a no-start issue often requires looking beyond just the relay:

  1. Confirm Fuel Pump Operation: Listen for the prime sound at key-on. No sound? Check relay + fuse + inertia switch. Sound present? Suspect pump failure or fuel line issues. Can be confirmed with fuel pressure testing.
  2. Check for Spark: Rule out ignition problems. A basic spark test (using a spark tester or carefully removing a plug wire) shows if the ignition coil and module are working.
  3. Scan for Diagnostic Trouble Codes (DTCs): Even if the "Check Engine" light isn't on, there might be pending codes stored in the PCM related to fuel delivery or sensor inputs causing a no-start. Using an OBD-II scanner can provide valuable clues.
  4. Check Battery Health: Ensure the battery has sufficient voltage and the terminals are clean and tight. A weak battery can crank the starter slowly but not provide enough power for the PCM or pump to function correctly.
  5. Listen for Engine Rotation: Ensure the starter is actually turning the engine over properly – listen for normal cranking speed. Slow cranking points to battery/starter issues.
  6. Security System: Some later models have PATS systems. A "THEFT" light flashing rapidly might indicate an immobilizer issue preventing fuel and spark.

Conclusion: Power, Position, and Practical Fixes

Locating the fuel pump relay in your 1998 Ford Explorer (#21 in the underhood Power Distribution Box) is a foundational skill for diagnosing frustrating no-start or stall conditions. By starting with the fuse (#1 in PDB), checking the inertia switch (passenger kick panel), and knowing how to access, inspect, and test relay #21 – including the simple but powerful swap test – you're equipped to resolve a very common problem quickly and confidently. Remember that the diagram on your PDB cover is your roadmap, matching replacement relays by part number is essential for reliability, and always re-secure the cover after work. While relay failure is frequent, use this process to verify it’s truly the culprit before concluding the pump itself needs replacement. Mastering this specific location empowers you to get your Explorer back on the road with minimal downtime.

Back to blog