The Unmistakable Answer: 2004 Honda Pilot Fuel Pump Relay Location - It's Under the Hood! (And Here's Exactly How to Find & Replace It)

For owners of the trusty 2004 Honda Pilot experiencing starting problems, the fuel pump relay location is consistently found in Position B within the main under-hood fuse and relay box. Pinpointing its exact spot is crucial when your Pilot cranks but refuses to start or exhibits other fuel pump-related symptoms. Knowing precisely where to look and how to handle this critical relay saves significant time and prevents unnecessary troubleshooting steps or costly trips to the mechanic for a relatively simple fix.

Recognizing Symptoms of a Failing Fuel Pump Relay

Before diving under the hood, it's essential to understand when the fuel pump relay might be the likely culprit. The relay acts as a switch, controlling the high current needed to power the fuel pump based on signals from the vehicle's computer. A malfunctioning relay prevents the pump from receiving power, leading directly to engine starting failure. Watch for these key indicators:

  • Engine Cranks But Does Not Start: The most classic symptom. The starter motor operates normally, turning the engine over, but the engine fails to ignite due to lack of fuel delivery.
  • No Fuel Pump Priming Sound: Listen carefully the moment you turn the ignition key to the "ON" position (before engaging the starter). A healthy fuel pump will produce a distinct humming or whirring sound for a few seconds as it pressurizes the fuel system. Absence of this sound strongly suggests a problem with the pump's power circuit – commonly the relay, fuse, or the pump itself.
  • Intermittent Starting Issues: A relay on the brink of failure might work occasionally and fail at other times. You might experience sporadic no-start conditions or hesitation when starting, seemingly at random.
  • Check Engine Light and Diagnostic Trouble Codes (DTCs): While not guaranteed, a failing fuel pump relay can sometimes trigger relevant trouble codes like P0230 (Fuel Pump Primary Circuit Malfunction) or other fuel delivery-related codes. A scan tool check is advisable if the light is illuminated, but the absence of a code doesn't rule out the relay.

Pinpointing the Under-Hood Fuse and Relay Box

The main fuse and relay box for engine-related components like the fuel pump relay is located in the engine compartment. For the 2004 Honda Pilot, follow these steps to find it:

  1. Open the Hood: Release the hood latch inside the cabin (usually found near the driver's side kick panel or door) and secure the hood using the provided prop rod.
  2. Locate the Box: Stand facing the front of the vehicle. Look on the driver's side (left side) of the engine bay, near the very back (closest to the windshield/firewall). It is a rectangular black plastic box, often the largest fuse box under the hood.
  3. Identify the Cover: The box has a plastic cover clearly labeled "FUSE & RELAY BOX" or similar. This cover needs removal to access the relays inside.

Finding Position B: The Fuel Pump Relay's Home

With the cover of the main under-hood fuse and relay box removed, identify the specific location for the fuel pump relay:

  1. Understand the Layout: The box contains numerous fuses and relays arranged in rows. Relays are typically larger, cube-shaped components compared to the smaller, flatter fuses. They plug into sockets.
  2. Locate Position B: On the inside of the fuse box cover you just removed, there is an accurate diagram or map showing the exact layout and identity of every fuse and relay position within the box. Crucially, find the relay labeled as "FUEL PUMP" or similar. The diagram on a 2004 Honda Pilot will explicitly assign this "FUEL PUMP" relay to a position labeled "B".
  3. Correlate with the Box: Place the cover beside the open fuse box and carefully locate the socket marked "B" within the box itself. The relay plugs into this socket.
  4. Visual Identification (Confirming): The fuel pump relay in the 2004 Pilot is typically a standard black cube-shaped relay, approximately 1 inch square. Look for the OEM or equivalent part number printed directly on the relay's plastic housing. The OEM Honda part number for the fuel pump relay in the 2004 Pilot is often FB8191-100. It is frequently referred to as a "5-pin" relay due to the number of terminals. Confirm it matches the position marked "B" and the label "FUEL PUMP" on the lid diagram.

(Optional but Recommended: Take a clear photo of your open fuse box for reference before proceeding further.)

Removing the Faulty Fuel Pump Relay: A Safe Step-by-Step Guide

Replacing the relay is a straightforward task that requires no special tools:

  1. Turn Off the Vehicle: Ensure the ignition is completely OFF.
  2. Disconnect the Negative Battery Terminal (Highly Recommended): Locate the negative battery terminal (marked with a "-" sign, often black). Loosen the nut/bolt securing the cable clamp to the terminal post using a standard wrench (usually 10mm), carefully slide the clamp off the post, and secure the cable away from the terminal to prevent accidental contact. This step prevents accidental shorts or sparks while working near electrical components.
  3. Locate Position B: Re-confirm the relay is positioned at the socket labeled "B" in the under-hood fuse box.
  4. Grasp the Relay: Firmly grasp the fuel pump relay body. Do not pull by any wires connected to it.
  5. Pull Straight Up: Apply steady, even pressure straight upwards (perpendicular to the fuse box base) to pull the relay out of its socket. Avoid rocking it side-to-side, as this can damage the socket. It should release with moderate force. Inspect the relay's terminals and the corresponding terminals in the socket for any signs of corrosion, melting, or damage – these issues should also be addressed.
  6. Identify the Replacement: Compare the removed relay's part number to the one listed earlier (FB8191-100 or equivalent). Ensure your new relay matches exactly.

Testing the Relay (Optional Verification)

While replacing a suspected bad relay is common practice, verifying its condition with a multimeter provides certainty:

  1. Set Your Multimeter: Switch the multimeter to the resistance (Ohms, Ω) setting.
  2. Identify the Control Circuit Terminals: Look at the bottom of the relay where the pins are. Refer to the diagram typically molded into the relay's plastic case:
    • Pin 85 and Pin 86: These are the terminals for the relay's electromagnetic coil (the control circuit).
    • Pin 30 and Pin 87: These are the main power switching terminals (the circuit it controls, in this case, the fuel pump power).
  3. Test the Control Coil:
    • Place one multimeter probe on Pin 85 and the other on Pin 86.
    • You should read a specific resistance value, typically between 50 and 120 Ohms for a healthy Honda relay of this type. An infinite (O.L. or Over Limit) reading indicates an open coil (bad relay). A reading near 0 Ohms indicates a shorted coil (bad relay).
  4. Test the Switching Contacts (Requires 12V Source - CAREFUL): This step involves applying 12V. If you are uncomfortable, skip it.
    • Connect Pin 85 to the positive terminal of a 12V power source (e.g., a small 12V battery).
    • Connect Pin 86 to the negative terminal of the same 12V source. You should hear/feel a distinct "click" as the relay energizes.
    • Set your multimeter to continuity or the lowest Ohms setting.
    • With the coil energized (12V applied to 85 and 86), place probes on Pin 30 and Pin 87. The multimeter should show continuity (near 0 Ohms). Without power to the coil, Pins 30 and 87 should show no continuity (infinite resistance / O.L.).
    • Failure to click or failure to show continuity when energized means the relay is faulty.

Installing the New Relay Correctly

  1. Position: Ensure the new relay aligns precisely with the socket at Position B in the fuse box. Relays have a specific orientation. Look for a small notch, tab, or marking on one side of the relay and a corresponding notch or guide in the socket. Misalignment can prevent installation or damage pins.
  2. Align and Insert: Carefully line up the pins on the bottom of the relay with the holes in the socket. Apply firm, straight downward pressure until the relay is fully seated and clicks or locks into place. It should fit snugly without excessive force. Double-check it is securely installed in the correct Position B.
  3. Reconnect the Battery: Securely reconnect the negative battery cable to its terminal and tighten the nut/bolt fully.
  4. Test Before Reassembly: Before putting the fuse box cover back on:
    • Turn the ignition key to the "ON" position (do not start the engine).
    • Listen attentively: You should clearly hear the fuel pump whir/hum for 2-3 seconds as it primes the system. This is the key sign the relay is working.
    • Attempt to start the engine. If the problem was solely the faulty relay, the engine should now start normally.
    • If the pump doesn't prime or the engine still doesn't start, further diagnosis is required (e.g., checking the fuel pump fuse, fuel pump itself, or ignition switch).

Replacing the Fuse Box Cover: Finalizing the Job

Once the new relay is confirmed working by the fuel pump priming sound and/or successful engine start:

  1. Ensure Ignition Off: Turn the key back to the OFF position.
  2. Align Cover: Position the plastic fuse box cover correctly over the box. It will typically have locating tabs or hooks at one end and securing clips at the other.
  3. Secure: Press down firmly on the cover, particularly where the securing clips are located, until it snaps or locks securely into place on all sides. Ensure it sits evenly and is properly sealed to protect the components inside from moisture and debris.

Understanding Relay Interchangeability and Sourcing Options

  • Standard Part: The Honda FB8191-100 fuel pump relay is a common, standardized automotive relay type used across many Honda and Acura models for years. While the mounting footprint is standard, always verify the exact part number against your old one or reliable sources.
  • Where to Buy: Replacement relays are widely available:
    • Honda Dealer Parts Department: Source the genuine Honda OEM relay (FB8191-100) for guaranteed compatibility.
    • Major Auto Parts Stores: Retailers like AutoZone, O'Reilly, Advance Auto Parts, NAPA, etc., reliably stock compatible equivalents from reputable aftermarket manufacturers (e.g., Standard Motor Products, Bosch, Tridon/HELLA). Ask for the relay for a 2004 Honda Pilot fuel pump. Online retailer catalogs (e.g., RockAuto) are also excellent resources.
    • Online Marketplaces: eBay, Amazon – exercise caution and purchase only from highly rated sellers known for automotive parts to avoid counterfeits.
  • Cost: The relay is an inexpensive component, typically costing between 25 USD.

Proactive Maintenance and Prevention

  • Keep the Box Clean and Dry: Periodically inspect the under-hood fuse and relay box for debris, water ingress (especially after heavy rain or washing), or signs of rodent damage. Ensure the cover is always properly sealed.
  • Consider a Spare: Given their critical role and relatively high failure rate compared to other components (especially as the vehicle ages), carrying a spare fuel pump relay specific to your Pilot (FB8191-100 equivalent) in your glove compartment is highly recommended. This provides an immediate solution if failure occurs away from home.
  • Prompt Diagnosis: If you experience symptoms like cranking without starting or silent priming, address them promptly. Continuously trying to start with a failed fuel pump relay puts unnecessary strain on the starter and battery.
  • Electrical Contact Cleaner: If corrosion is found on relay terminals or sockets during inspection, use a dedicated electrical contact cleaner spray (followed by careful brushing if needed) to clean the contacts before installing a new relay. Allow to dry thoroughly.

When the New Relay Doesn't Solve the Problem

A new relay failing to restore function indicates another underlying issue within the fuel pump circuit:

  1. Inspect the Fuel Pump Fuse: Locate the "FUEL PUMP" fuse within the same under-hood fuse and relay box. Consult the lid diagram. Pull it out (using the supplied fuse puller tool in the box) and inspect the metal strip inside. A broken or melted strip indicates a blown fuse needing replacement. Crucially, find and fix the cause of the blown fuse (short circuit, failing pump). Simply replacing a blown fuse without addressing the cause will likely result in it blowing again immediately.
  2. Test the Fuel Pump Itself: If the fuse is good and the relay clicks/primes, but the engine still doesn't start, the fuel pump itself may be faulty. This requires more advanced diagnosis and potentially fuel system work. Listen inside the fuel filler neck with the cap removed when the ignition is turned ON – you should hear the pump inside the tank. Lack of sound after confirming relay/fuse is good points to a bad pump or wiring issue.
  3. Check Related Wiring/Connections: Inspect wiring harnesses related to the fuel pump relay socket, fuse, and leading to the fuel pump for damage, chafing, or loose connections, especially around connectors near the fuel tank or under the vehicle.
  4. Ignition Switch Issues: A malfunctioning ignition switch might not be sending the signal to energize the fuel pump relay. Testing usually requires a wiring diagram and multimeter.
  5. ECM/PCM Concerns: In rare cases, the engine control module might fail to command the relay to activate. Professional diagnosis is needed here.

Knowing the precise location of the 2004 Honda Pilot fuel pump relay (Position B in the main under-hood fuse box) and how to replace it is fundamental knowledge for any owner tackling starting issues. This straightforward repair can resolve common problems efficiently and economically. Remember the key steps: locate the under-hood box, identify Position B using the lid diagram, replace the relay (FB8191-100 or equivalent), and listen for the reassuring priming sound as confirmation. By understanding the symptoms and having a spare relay on hand, 2004 Pilot owners are well-equipped to ensure their reliable SUV keeps running smoothly.

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