1999 Ford Expedition Fuel Pump Relay Location: Your Complete Guide (Diagnosis, Access & Replacement)

The fuel pump relay in your 1999 Ford Expedition is located in the Central Junction Box (CJB), also known as the main power distribution box, under the hood, near the brake master cylinder. Look for relay position #12. It's a standard black or gray cube-shaped relay, typically with 4 or 5 blade terminals on the bottom. Before digging in, it's crucial to correctly identify symptoms pointing to a potential fuel pump relay failure to avoid unnecessary work.

Symptoms of a Failing Fuel Pump Relay (1999 Ford Expedition)

Listen carefully to your vehicle. Recognizing the early warning signs saves time and frustration:

  1. Engine Cranks But Won't Start: This is the classic symptom. You turn the key, the starter motor spins the engine normally (cranking), but the engine never fires up. It sounds like the engine is trying to turn over but doesn't "catch" because fuel isn't reaching the injectors.
  2. No Fuel Pump Prime Sound: When you first turn the ignition key to the "ON" position (before cranking to start), you should hear a distinct humming or buzzing sound lasting 1-2 seconds from the rear of the vehicle (near the fuel tank). This is the fuel pump pressurizing the system. If you hear NO sound at all during those first few seconds in the "ON" position, a failed relay (or fuse or pump) is a top suspect. Note: Listen carefully; the sound can be faint, especially in noisy environments.
  3. Intermittent Starting Problems: Your Expedition might start perfectly fine one day and refuse to start the next. Or it might struggle to start after being parked briefly but starts easily when cold. These unpredictable symptoms often point to a relay that's losing contact internally due to heat, wear, or corrosion – it works sometimes and fails other times.
  4. Engine Stalls While Driving: A relay that cuts out intermittently while driving can cause the engine to suddenly stall as if you turned the key off. The electrical connection to the pump is lost, starving the engine of fuel instantly. In some cases, it might restart immediately after stalling; in others, you'll need to wait.
  5. Stalling Under Specific Conditions: Pay attention if stalling happens more frequently when the engine is hot, when driving over bumps, or when using electrical accessories like headlights, A/C, or power windows. Heat and vibration stress failing relays, and increased electrical load can sometimes expose weak connections.

Function: Why the Fuel Pump Relay is Critical in Your 1999 Expedition

Understanding the relay's purpose helps you grasp its importance and pinpoint problems:

  1. High Current Requirement: The fuel pump motor requires significant electrical current (amperage) to operate. This is far too much current for the ignition switch itself to handle safely and reliably.
  2. Electrical Protection: The relay acts as a heavy-duty switch. It uses a small, low-current electrical signal from the Powertrain Control Module (PCM) or the ignition switch (controlled by the PCM) to control the flow of the large current needed to power the fuel pump.
  3. Safety and Logic Control: The relay allows the vehicle's computer to turn the fuel pump on only when necessary. It powers the pump for a few seconds when you first turn the key to "ON" to prime the system. It keeps the pump running while the engine is cranking and running. Crucially, it shuts the pump off immediately if the engine stalls or if the key is turned "ON" without cranking (after that initial prime) – this is a critical safety feature.
  4. Preventing Ignition Switch Damage: By handling the heavy lifting for the fuel pump circuit, the relay prevents the ignition switch contacts from burning out prematurely due to carrying the high pump current directly.

Finding the Relay Location & Physical Identification

Now that you understand the symptoms and function, let's locate and identify the relay precisely:

  1. Open the Hood: Securely prop the hood open. You'll be working under the hood.
  2. Locate the Central Junction Box (CJB): Look for a large, usually black plastic box on the driver's side of the engine compartment. It is positioned near the brake master cylinder (the component the brake fluid reservoir sits on) and the firewall (the vertical metal wall separating the engine compartment from the cabin). Some earlier model year 2nd-gen Expeditions have it closer to the battery. If uncertain, trace the thick positive battery cable; it will lead to this box.
  3. Remove the CJB Cover: The cover is secured by plastic clips. Squeeze these clips inward and lift the cover off. Set the cover aside safely where it won't fall into moving parts. The underside of the cover usually has a detailed diagram showing relay and fuse locations and their amperage ratings. Find Position #12 on this diagram. It's usually labeled "Fuel Pump Relay," "FP Relay," or similar.
  4. Identify Relay #12: Inside the box, look for the relay sockets corresponding to the diagram. Relay sockets are typically arranged in rows. Locate the socket labeled #12. There might be a small number molded into the plastic near the socket, or you'll need to count positions starting from a known reference (like position #1). The relay itself is a small, cube-shaped component, typically black or gray, about the size of a standard matchbox or slightly smaller. It will have 4 or 5 thin metal blade terminals sticking out of its base that plug into the socket. Visually compare it to the other relays nearby; most look identical. Its position (#12) is the definitive identifier, not its looks.
  5. Important Clarification: Relay in Engine Bay, Pump Near Tank: Remember, the relay is under the hood. The actual fuel pump is submerged inside the fuel tank at the rear of the vehicle. Don't confuse the two locations.

How to Access and Remove the Relay (1999 Ford Expedition)

Removing the relay is straightforward. Power tools are unnecessary; avoid excessive force.

  1. Verify Key Position: Ensure the ignition key is in the "OFF" position. Remove the key for maximum safety. Turn off all accessories.
  2. Locate Relay #12 (See Above): Confirm you have identified the correct socket within the CJB.
  3. Grasp Firmly: Firmly grasp the body of the fuel pump relay with your fingers. Avoid pulling by the wires or terminals (they are internal).
  4. Pull Straight Up: Gently but firmly pull the relay straight upward and out of its socket. It should release with moderate force. If it feels stuck, wiggle it very slightly (front-to-back or side-to-side, not twisting) while pulling upwards. Do not pry with screwdrivers! This risks cracking the CJB housing or damaging the socket contacts.
  5. Inspect: Look at the relay and socket. Are there signs of melted plastic, severe corrosion, or burnt smells? Note any discoloration or damage.

Checking the Associated Fuses (Essential Step!)

A blown fuse can cause identical symptoms to a bad relay. NEVER skip checking the fuses first!

  1. Consult CJB Cover Diagram: Look at the underside of the CJB cover. Identify the fuses related to the fuel pump circuit. Crucially, find fuse #13 (20 Amp Mini fuse), often labeled "Fuel Pump," "Fuel Pump Relay," or "FP." There might be other larger fuses (like fuse #1, 50 Amp) powering the entire CJB where the relay socket gets its feed, but fuse #13 is the primary one protecting the relay's switched output circuit to the pump itself.
  2. Visually Inspect Fuses: Using the plastic fuse puller tool (usually clipped inside the CJB or in the glove box), carefully remove fuse #13. Hold it up to a light source. Examine the thin metal wire element inside the clear plastic body. If the wire is broken, separated, or visibly melted/blackened, the fuse is blown. Replace it with an exact duplicate (same amp rating, 20A Mini fuse). Blown fuses indicate an overload elsewhere in the circuit (like a failing pump motor).
  3. Also Check CJB Fuse #1 (50A Maxi Fuse): While less common to blow solely for the fuel pump circuit, it powers the relay's input side. Verify its integrity visually (look for a broken metal strip element in the large Maxi fuse).
  4. Reinstall Fuses Securely: Press good fuses or new replacements fully into their sockets until they seat firmly.

Testing the 1999 Expedition Fuel Pump Relay (Swap Test)

The most practical test is the relay swap. You often have identical relays:

  1. Identify a Suitable Swap Candidate: Find another relay in the CJB that looks identical (same physical size, same number of terminals, often same color) and controls a non-critical function. Common swap choices for #12 include the horn relay (sometimes #14), the A/C compressor clutch relay, or the blower motor relay (HVAC fan - might be labeled "Blower" or "Htd Backlite" on some diagrams). DO NOT swap with critical relays like PCM Power, Injector Power, Ignition Coil Power, or Starter Solenoid. Consult your CJB cover diagram.
  2. Perform the Swap: Remove the relay you identified as a good candidate. Note its position.
  3. Install Candidate Relay into #12: Take this known good relay and install it securely into the #12 fuel pump relay socket.
  4. Listen for Fuel Pump: Turn the ignition key to the "ON" position (do not crank). Listen carefully near the rear of the vehicle. Do you hear the fuel pump prime sound (1-2 second hum/buzz)? If you hear the prime sound now, whereas you didn't before, it strongly indicates your original relay in position #12 was faulty.
  5. Check Starting: If the prime sound returns, try starting the engine. If it starts and runs, this confirms the original relay was the culprit.
  6. Test the Original Relay (Optional): Place the suspect relay into the socket where the good swap relay came from. Test the function controlled by that socket (e.g., honk the horn, run the A/C, turn on the blower fan). If the function doesn't work with the suspect relay in place, it confirms the relay is bad.
  7. Important Considerations: This test is very reliable if the prime sound returns after the swap. If the prime sound still doesn't occur after putting a known good relay in position #12, the problem likely lies elsewhere: a blown fuse (#13!), a wiring fault between the CJB and the pump (corrosion, break), a bad fuel pump, a failed inertia switch (see below), or a PCM control signal issue.

Replacing the Fuel Pump Relay (1999 Ford Expedition)

Replacement is simple:

  1. Obtain Correct Replacement Relay: Purchase a new relay. Ford's original part number was F57B-14B192-AA or similar. Crucially, match the relay specifications:
    • Physical size/shape.
    • Number of terminals (4 or 5 pins - 5-pin is a bit more common for the fuel pump circuit in the Expedition). A 5-pin relay can work in a 4-pin socket (the extra "87a" terminal is unused), but a 4-pin relay cannot plug into a 5-pin socket. Buying the correct OEM terminal count (usually 5-pin, confirm visually!) ensures optimal fit.
    • Terminal configuration (pin spacing and layout - should match the sockets in the CJB).
    • Amperage/Current Rating (typically 20-30 Amp switching capacity for fuel pumps). Most aftermarket relays are adequate (e.g., Bosch 0332019150 or a standard "Micro Relay").
    • Confirm it's intended for automotive use (ISO type).
  2. Install: Ensure the new relay is oriented correctly (the terminals will only fit the socket one way). Align the blades with the socket holes and press the relay firmly and squarely down until it seats fully and you feel it click or lock in place. Give it a gentle tug to confirm it's secure.
  3. Test: Turn the ignition key to "ON" and listen for the fuel pump prime sound. Attempt to start the engine. If it starts and runs normally, the replacement was successful.

Don't Forget the Fuel Pump Inertia Safety Switch!

This is another vital safety component often overlooked:

  1. Purpose: The inertia switch cuts power to the fuel pump during a significant impact (collision). Its goal is to prevent fire by stopping fuel flow from the pump if the vehicle is hit hard.
  2. Location (1999 Expedition): Inside the passenger compartment. On this model year, it's located on the passenger side footwell, mounted vertically just forward of the kick panel, below the carpet level against the firewall. You might need to lift the carpet edge slightly near the kick panel to find it. It's a small, usually red or black plastic box (roughly the size of a deck of cards) with a prominent rubber reset button on top.
  3. How it Causes Problems: A hard bump (like hitting a severe pothole, curb, or minor collision) can trip the switch. It can also sometimes trip due to vibration or weak mounting over time.
  4. Symptom: Identical to a bad fuel pump or relay - car cranks but won't start, no fuel pump prime sound.
  5. Check & Reset:
    • Locate the switch (passenger footwell against firewall).
    • Press the reset button firmly on the top of the switch. You might hear a faint click. Ensure the button is fully seated down.
    • Check for the fuel pump prime sound (ignition "ON"). Try starting the engine.
  6. Trip Condition: If the button was popped up, resetting it is the solution. If the button was already down and resetting it doesn't restore function, the switch itself or its wiring could be faulty (or the problem is elsewhere).

When the Issue Might Not Be the Relay

Consider these possibilities if replacing the relay doesn't fix the problem:

  1. Faulty Fuse: Re-check fuses #13 (20A) and #1 (50A) in the CJB – a brand new fuse could blow immediately if there's an underlying short circuit.
  2. Bad Fuel Pump: The pump motor itself is the most common failure point after the relay and fuses. Requires tank access/replacement.
  3. Wiring Harness Problems: Corrosion, damage, or loose connections in the wiring between the CJB relay and the fuel pump (especially at connectors under the vehicle), at the pump connector itself, or even within the CJB socket.
  4. Failed Inertia Switch: As described above – tripped, faulty, or damaged wiring to the switch. Check and reset.
  5. Ignition Switch Fault: If the signal telling the relay to turn on isn't being sent properly from the ignition switch or PCM.
  6. PCM Malfunction: Rare, but the PCM module that commands the relay to turn on could have an internal problem preventing the control signal.

Conclusion & Final Tip

The fuel pump relay (located in position #12 in the under-hood Central Junction Box) is a common failure point causing a no-start condition in your 1999 Ford Expedition. Diagnosis involves listening for the missing fuel pump prime sound and performing a simple relay swap test. Always check the related fuses (especially #13) and the inertia switch before condemning the pump itself. Replacing the relay is a quick and inexpensive repair you can do yourself with basic tools. If replacing the relay, confirming the fuses are good, and resetting the inertia switch doesn't resolve the issue, further diagnosis of the wiring harness or fuel pump itself will be necessary. Accurate diagnosis saves time and money.

Back to blog