03 Ford Explorer Fuel Pump Relay Location: Find It Fast to Fix No-Start Issues

The fuel pump relay location in a 2003 Ford Explorer is found in the Battery Junction Box (BJB) under the hood, near the driver's side front fender. Look for relay position #10 (usually labeled "Fuel Pump") within that large black fuse/relay box.

If your 2003 Ford Explorer cranks but won't start, a dead fuel pump is a prime suspect. And often, the culprit isn't the pump itself but the electrical component controlling it: the fuel pump relay. Knowing exactly where to find this critical relay saves time, money, and frustration during diagnosis. For the 2003 model year, its location is consistent and relatively straightforward under the hood.

Finding the Battery Junction Box (BJB)

Your first destination is the engine compartment. Open the hood and secure it safely. Position yourself near the driver's side front fender.

  • Look Locally: Direct your attention to the area immediately behind the vehicle's battery. The Battery Junction Box (BJB) is a large, rectangular, black plastic box. It's the main underhood fuse and relay panel housing dozens of fuses and several critical relays.
  • Identify the Box: The BJB has a removable black plastic lid. This lid is essential as it holds a printed diagram or listing showing the function and location of every fuse and relay contained inside the box. Do not start pulling relays without identifying this lid first.
  • Remove the Lid: Press the securing clips (usually one or two at each end) and carefully lift the entire lid straight off the BJB. Set it aside gently to prevent damage.

Identifying Relay Position #10 (Fuel Pump Relay)

With the BJB lid removed, you'll see numerous fuses (smaller, often colored components) and a handful of larger, typically cube-shaped relays plugged into specific sockets. The specific relay position matters more than the relay's appearance at this stage.

  • Locate the Position Diagram: Flip the BJB lid you just removed over. Its underside features a detailed map or chart. This chart corresponds exactly to the layout of the fuse and relay sockets inside the box itself. It lists numbers, component names (or abbreviations), and sometimes even the amperage ratings for fuses.
  • Find #10 Fuel Pump: Scan this diagram carefully. Look for a relay position labeled "#10" (or sometimes simply "10"). Its function should be clearly marked as "Fuel Pump" or "FP". This identification is absolute. You are looking for the socket designated position #10.
  • Position Confirmation: Compare the diagram's layout with the actual sockets in the BJB. Position counting usually follows a logical grid pattern (rows and columns). Verify that the socket you are looking at is indeed position #10 according to the diagram. This is the only relay position designated for the fuel pump circuit in the primary underhood BJB for the 2003 Explorer.

The Fuel Pump Relay Itself

Once you've identified the correct socket (#10), look at the relay plugged into it.

  • Physical Description: The fuel pump relay itself is a standard automotive mini-ISO relay. It's a small, black (or sometimes slightly translucent), mostly cube-shaped component, roughly 1 inch x 1 inch x 1 inch in size. It has multiple prongs (terminals) on its underside that plug into the socket.
  • Visual Confirmation: While the relay should be the one labeled "Fuel Pump" in position #10, it's always good to double-check any markings on the relay body itself. You might see faint printing indicating "FPDM" (Ford Pump Driver Module) or a Ford part number like 1U2Z-14S411-BA (or equivalents), but don't rely solely on this – the socket position #10 is the definitive identifier. The primary marking is its position according to the diagram.
  • Function: This relay receives a low-power signal from the Powertrain Control Module (PCM) when you turn the ignition key to the "Run" or "Start" position. It acts as a heavy-duty switch, allowing full battery power to flow through the larger terminals to the fuel pump assembly located inside the fuel tank. Without this relay closing its internal contacts, the fuel pump gets no power and the engine cannot start.

What If Nothing is in Position #10?

Finding an empty socket in position #10 is highly unusual. Unless the relay has been physically removed during troubleshooting (or fallen out, which is rare), it should be present. A missing relay points to an incomplete prior repair or significant tampering. Verify you are looking at the correct position via the diagram.

Why Knowing This Location is Crucial (Beyond Just Finding It)

Understanding where the relay is located is the first step. Its location matters significantly for:

  1. Rapid Diagnosis: A failed relay is a common cause of "cranks but won't start" conditions. Swapping the fuel pump relay with another identical relay (like the horn relay) in the BJB is the fastest, zero-cost diagnostic test. If the Explorer starts after swapping, you know the original fuel pump relay is faulty. Knowing its exact location (#10) allows you to perform this swap in seconds.
  2. Testing Accessibility: Physically accessing the relay is required for both swapping testing and potentially using a multimeter to check its activation signal and switching function. Position #10 is generally easily reachable.
  3. Repair Efficiency: Replacing a bad relay is far simpler and cheaper than dropping the fuel tank to replace the pump itself. Knowing the precise location means you can quickly purchase a replacement relay, plug it into socket #10, and resolve the issue.
  4. Safety Checks: In the rare event of needing to disable the fuel system (e.g., for certain repairs), pulling the fuel pump relay from position #10 immediately cuts power to the fuel pump, allowing fuel pressure to depressurize safely without the pump running.

Are There Other Relays for the Fuel Pump in a 2003 Explorer?

No, for the 2003 Ford Explorer 4-door (both 2WD and 4WD variants), the primary control for the fuel pump power circuit is exclusively the relay located in the underhood BJB at position #10. Here's why confusion might arise:

  • Shifted Locations: Earlier second-generation Explorers (1995-2001) used significantly different fuse/relay layouts. Their fuel pump relay was often located in the Central Junction Box (CJB), mounted near the parking brake pedal under the dashboard. However, the 2003 Explorer follows the position #10 in the BJB standard for its model year group (2002-2005).
  • Inertia Switch: The fuel system does have an inertia safety switch (usually located in the passenger footwell, behind a trim panel near the kick panel or under the glovebox). This is a circuit interruptor, not a relay. If triggered (e.g., in a collision or severe impact), it cuts power to the fuel pump relay, but the relay itself is still the primary component in the BJB.
  • Fuel Pump Driver Module: Starting around 2002, Ford began integrating the Fuel Pump Driver Module (FPDM) into some vehicles to provide variable voltage control for pump speed (leading to quieter operation). This module receives commands from the PCM, but its power feed is still controlled by the main power relay located in the underhood BJB, position #10. The FPDM is a separate module, often mounted elsewhere (e.g., near the spare tire), but it works downstream of the #10 relay. If relay #10 fails, the FPDM gets no power.

Symptoms of a Faulty Fuel Pump Relay (2003 Explorer)

Knowing where the relay is helps most when you experience these classic symptoms:

  • Engine Cranks But Will Not Start: The most common sign. The starter spins the engine (cranks), but the fuel pump isn't running to deliver fuel. A quick relay check is essential.
  • Intermittent Starting Problems: The engine might start sometimes but not others, especially when hot, pointing to a failing relay with internal heat-sensitive issues.
  • Silence During Key-On: When you first turn the ignition key to the "Run" (not "Start") position, you should hear the fuel pump whirr for a few seconds (pressurizing the system). If there is no audible whine from the rear of the vehicle, it strongly suggests no power is reaching the pump, potentially due to a bad relay or fuse. Listen near the rear undercarriage/fuel tank area.
  • Check Engine Light: While not always present for a pure relay failure, it's possible for the PCM to detect a circuit issue related to the relay command, potentially setting a P0230 code (Fuel Pump Primary Circuit Malfunction) or other related fault codes.

Basic Steps for Testing the Relay (Swap Test)

The easiest test relies on knowing the location (#10) and finding an identical relay:

  1. Find Relays: Identify relay #10 (Fuel Pump). Then, identify another relay in the BJB that uses the exact same physical relay type. Common good candidates are the High Beam Headlamp Relay (Position #9) or the Horn Relay (Position #7). Consult the BJB lid diagram to confirm these are standard mini-ISO relays like the fuel pump relay. Crucial: Only swap with a relay that the diagram shows uses the same part number/symbol as #10 and controls a non-critical circuit if it sticks on (horn/high beams are okay, ABS/powertrain are not).
  2. Swap: Carefully grasp both relays and pull them straight up and out of their sockets. Plug the known-good relay (e.g., the horn relay) into the fuel pump relay socket (position #10). Plug the suspected bad fuel pump relay into the horn relay socket.
  3. Test: Try starting the engine. If the engine starts and runs normally, you have confirmed the original fuel pump relay is faulty. If the problem persists (no start, no fuel pump whine), the issue lies elsewhere (fuse, wiring, pump, FPDM, PCM, inertia switch). Remember to swap the relays back to their original positions once testing is complete.

Important Safety Precautions

  • Vehicle Off: Always ensure the ignition is OFF and the key is removed before touching any relays or fuses. Work on the Battery Junction Box only when the engine is completely off.
  • Fire Risk: The BJB carries high amperage battery power. Avoid dropping metal tools into the box or causing accidental short circuits. Keep the area clean and dry.
  • Hot Components: Be cautious if the engine is hot. Let it cool down before working under the hood.
  • Accidental Activation: If testing relays by swapping, remember that swapping a relay into a different position (like #10) means that circuit (the horn, in our example test) will now be temporarily controlled by the suspect relay. Be aware you might accidentally sound the horn briefly during removal/insertion if the key is turned to "Run".
  • Correct Replacement: If replacing the relay, use a relay specified for that socket (standard automotive mini-ISO relay) with matching specifications. Confirm compatibility with the Motorcraft F7CF-14B192-AA relay or an equivalent high-quality aftermarket replacement suitable for automotive fuel pumps. Avoid cheap, low-quality relays.

What Else If the Relay Checks Out?

If swapping the relay made no difference (engine still doesn't start, fuel pump still silent), further investigation is needed:

  1. Check Fuel Pump Fuse: The fuel pump circuit has a main power fuse. Again, check the BJB lid diagram. For a 2003 Explorer, the main fuel pump fuse is typically Fuse #6 (20 Amp Mini Fuse) located within the same Battery Junction Box (BJB) as the relay. Visually inspect the fuse element – a broken element means it's blown. Replace with an identical 20A fuse. A blown fuse indicates a potential short circuit downstream that needs investigation.
  2. Listen for the Pump: Double-check for the initial 2-3 second fuel pump whine when turning the key to "Run". Have a helper turn the key while you listen near the fuel tank filler neck or rear seat area. No sound points strongly to a power or ground issue in the pump circuit (fuse, relay, inertia switch, wiring, FPDM, or pump).
  3. Inertia Switch: Locate the inertia switch in the passenger footwell. Press its reset button firmly. A tripped switch is an easy fix. However, if it trips repeatedly, there's a problem causing it to trigger unnecessarily.
  4. Voltage Checks: Diagnosing deeper often requires a digital multimeter (DMM). This involves:
    • Confirming power and ground at the relay socket (#10) during key-on/start.
    • Checking for power output from the relay socket (#10) during start/cranking when a known-good relay is inserted.
    • Checking for power at the inertia switch.
    • Checking for power at the Fuel Pump Driver Module (FPDM), if equipped, and at the pump connector (often requires accessing near the tank).
  5. Pump, Wiring, FPDM, or PCM: If power reaches the FPDM but not the pump, the FPDM or its ground circuit could be faulty. If power reaches the pump, but it doesn't run, the pump itself is likely dead. Broken wires or corroded connectors between components are also common failure points. PCM failure commanding the relay is rare but possible.

Conclusion: Power Lies at Position #10

For the owner or mechanic troubleshooting a no-start condition on a 2003 Ford Explorer, pinpointing the fuel pump relay location - specifically in the Battery Junction Box (BJB) under the hood, at position #10 - is the essential first step. Its accessibility allows for the quick and crucial swap test, potentially saving hours of unnecessary work and confirming a simple relay failure. Memorizing this position and understanding its function unlocks the most straightforward path to diagnosing and resolving one of the most common causes of a silent fuel pump and an Explorer that cranks but refuses to start. Keep that BJB lid diagram handy – it's your definitive guide to navigating the Explorer's electrical heart.

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