2004 Honda Pilot Fuel Pump Relay: Complete Location, Testing, and Replacement Guide

The bottom line: The 2004 Honda Pilot fuel pump relay is located inside the passenger compartment fuse box under the dashboard on the driver's side. It is labeled as the #1 fuse position (15-amp circuit) and is technically part of the PGM-FI Main Relay No. 2 assembly, which controls power delivery to the fuel pump . If your Pilot cranks but won't start, or stalls unexpectedly, a faulty fuel pump relay is one of the first things you should check before assuming the fuel pump itself has failed.

Understanding What the Fuel Pump Relay Does

The fuel pump relay acts as an electrical switch that sends power from your battery to the fuel pump when you turn the ignition key to the "ON" position. Without this relay working properly, the fuel pump won't receive power, and your engine won't get the fuel it needs to run .

On the 2004 Honda Pilot, this relay is not a standalone unit sitting by itself. It is integrated into a larger relay assembly called the PGM-FI Main Relay No. 2 (also referred to as the fuel pump main relay) . This assembly contains multiple relays in one plastic housing, and one of those internal relays is specifically responsible for the fuel pump circuit.

Where Exactly Is the Fuel Pump Relay Located?

Your 2004 Honda Pilot has two main fuse and relay boxes :

1. Engine Compartment Fuse Box – Located under the hood on the passenger's side of the engine bay, near the firewall. This box handles high-current circuits like the cooling fan, headlights, and main power distribution .

2. Interior Fuse Box (Driver's Side) – Located under the dashboard on the driver's side, near the kick panel. This is where the fuel pump relay lives .

Step-by-Step Instructions to Find the Fuel Pump Relay

Step 1: Sit in the driver's seat and look under the dashboard, just above your left foot rest area.

Step 2: Locate the rectangular plastic fuse box cover. It may have a small tab or latch you need to press to release it.

Step 3: Remove the cover and look at the diagram printed on the inside of the cover. This diagram shows the position of every fuse and relay in that box .

Step 4: Identify the #1 fuse position (15A) labeled "Fuel Pump" – this is the fuse for the fuel pump circuit. The actual relay is part of the PGM-FI Main Relay No. 2 assembly, which is usually a larger rectangular component plugged into the relay section of the same fuse box .

Step 5: The PGM-FI Main Relay No. 2 is often the only multi-relay block in that fuse box. It typically has five pins and is larger than a standard single relay. On the 2004 Pilot, this relay block controls both the fuel pump and some engine control functions .

Important Note: Some 2004 Pilot models may have slight variations depending on production date and trim level. If you cannot find the relay using these instructions, always refer to the diagram on your specific fuse box cover or consult your owner's manual .

Common Symptoms of a Bad Fuel Pump Relay

Before you start testing, here are the telltale signs that your fuel pump relay may be failing:

1. Engine Cranks But Won't Start – This is the most common symptom. You turn the key, the starter motor spins the engine, but it never fires up because no fuel is reaching the injectors .

2. Intermittent Stalling – The engine runs fine for a while, then suddenly dies without warning. After sitting for a few minutes, it may start again. This points to a relay that is failing internally due to heat or vibration.

3. No Fuel Pump Priming Sound – When you turn the ignition key to the "ON" position (without cranking), you should hear a brief humming sound from the rear of the vehicle. That's the fuel pump pressurizing the system. If you don't hear that sound, the relay may not be sending power to the pump.

4. Engine Starts Then Dies Immediately – The relay may provide power momentarily but then loses connection, causing the engine to start and stall right away.

How to Test the Fuel Pump Relay

Testing the fuel pump relay does not require expensive diagnostic tools. Here are the most practical methods for a DIY mechanic.

Method 1: The Swap Test

This is the easiest and quickest method :

  1. Locate the PGM-FI Main Relay No. 2 in the driver's side interior fuse box.
  2. Find another relay of the same type and pin configuration in the same fuse box. The starter cut relay or the A/C clutch relay are often the same type.
  3. Swap the suspect relay with the known-good relay.
  4. If the engine now starts and runs, the original relay was faulty.
  5. If the engine still won't start, the problem lies elsewhere.

Method 2: Listen for the Fuel Pump

  1. Turn the ignition key to the "ON" position but do not crank the engine.
  2. Listen carefully from the rear of the vehicle (near the fuel tank) for a 2-3 second humming sound.
  3. If you hear the hum, the relay and fuel pump are likely working. If you don't hear anything, the relay or pump has a problem.

Method 3: Using a Multimeter

If you have a multimeter, you can check for voltage at the relay:

  1. With the ignition in the "ON" position, probe the relay output terminal (consult your fuse box diagram for pin assignments).
  2. You should see battery voltage (around 12 volts) at the output pin for a few seconds when the ignition is first turned on.
  3. If you see no voltage, the relay may not be receiving a trigger signal, or the relay itself is faulty.

Fuel Pump Fuse vs. Relay: What's the Difference?

Many owners confuse the fuel pump fuse with the fuel pump relay. They serve different purposes:

Fuel Pump Fuse (15A, Position #1 in the driver's side interior fuse box) – The fuse protects the circuit from electrical overload. If the fuse is blown, the fuel pump loses power entirely. A blown fuse usually indicates a short circuit or a failing fuel pump drawing too much current .

Fuel Pump Relay (Part of PGM-FI Main Relay No. 2) – The relay is the switch that turns the fuel pump on and off. It can fail mechanically (sticking contacts) even if the fuse is perfectly fine.

Rule of thumb: Always check the fuse first. A visual inspection takes seconds. If the fuse is good but the pump isn't running, the relay is the next suspect.

Replacement Part Numbers for the 2004 Honda Pilot Fuel Pump Relay

If you determine the relay needs replacement, here are the genuine and aftermarket part numbers:

Genuine Honda Part Number: 39794-S5A-003 (also supersedes 39794-SDA-004)

Aftermarket Cross-Reference: Standard Ignition RY-726, 1R1414, 20068, 203-0199, 25-0386, AR6231, R6231, RAA1767

Vehicle Fitment: The 39794-S5A-003 relay fits the 2004 Honda Pilot, as well as many other Honda and Acura models from 2001 through 2009, including the Honda CR-V, Civic, Element, S2000, and Acura MDX .

Step-by-Step Replacement Procedure

Replacing the fuel pump relay assembly is straightforward:

  1. Disconnect the battery – Disconnect the negative terminal to prevent any electrical shorts while working near the fuse box .
  2. Locate the relay – Open the driver's side interior fuse box and find the PGM-FI Main Relay No. 2.
  3. Remove the old relay – Carefully pull the relay block straight out. It is held in by friction; you may need to wiggle it gently to free it .
  4. Install the new relay – Push the new relay block firmly into the slot until it is fully seated.
  5. Reconnect the battery – Reconnect the negative terminal.
  6. Test the vehicle – Turn the ignition to the "ON" position and listen for the fuel pump priming sound. Then start the engine and verify it runs smoothly .

Other Common Relays on the 2004 Honda Pilot

The 2004 Pilot uses multiple relays in both fuse boxes. Here are the most important ones you might encounter :

1. PGM-FI Main Relay No. 1 – Controls power to the engine control module (ECM/PCM) and fuel injectors. Located next to Main Relay No. 2.

2. Starter Cut Relay – Prevents the starter from engaging unless the transmission is in Park or Neutral. Located in the driver's side interior fuse box.

3. A/C Compressor Clutch Relay – Controls the air conditioning compressor. Located in the engine compartment fuse box.

4. Cooling Fan Relays – Control the radiator and condenser cooling fans. Located in the engine compartment fuse box.

5. Rear Blower Motor Relay – Controls the rear cabin heater/AC fan. Located in the driver's side interior fuse box.

What If Replacing the Relay Doesn't Fix the Problem?

If you replace the fuel pump relay and your Pilot still won't start or runs poorly, the issue could be with other components in the fuel delivery system :

1. Faulty Fuel Pump – The fuel pump itself may have failed. It is located inside the fuel tank and requires partial tank removal to replace. A failing fuel pump may still make noise but cannot deliver adequate fuel pressure.

2. Clogged Fuel Filter – A restricted fuel filter can mimic a bad pump or relay by preventing sufficient fuel flow. The 2004 Pilot's fuel filter is part of the fuel pump assembly and is not serviceable separately in most cases.

3. Fuel Injector Problems – Dirty or failing injectors can prevent fuel from entering the cylinders properly.

4. Wiring or Connection Issues – Corroded connectors, broken wires, or poor ground connections between the relay and the fuel pump can cause intermittent failures.

5. Crankshaft Position Sensor – A faulty crankshaft position sensor can prevent the ECM from triggering the fuel pump relay, even though the relay itself is good .

6. ECM/PCM Failure – In rare cases, the engine control module fails to send the signal to engage the fuel pump relay.

Preventive Maintenance Tips

To avoid being stranded by a fuel pump relay failure:

  • Listen for the prime – Every time you get in the Pilot, turn the key to the "ON" position and listen for the fuel pump hum. If it ever sounds weak or absent, investigate immediately.
  • Keep the relay area clean – Moisture and dirt in the fuse box can accelerate relay contact corrosion. Make sure the fuse box cover is properly installed.
  • Replace proactively – If you are replacing the fuel pump for any reason, consider replacing the relay at the same time. Both components tend to fail around the same mileage.
  • Use genuine or high-quality aftermarket parts – A cheap relay may not handle the current load reliably.

Why the 2004 Honda Pilot Fuel Pump Relay Location Matters

Understanding where the relay is and how to test it saves you time and money. A dealership diagnostic fee for a "no-start" condition can easily exceed $150, and they often replace the fuel pump first. By checking the relay and fuse yourself, you can eliminate the simplest and cheapest cause before spending hundreds on parts you may not need.

The fuel pump relay on the 2004 Pilot is accessed without any special tools, and replacement takes about 10 minutes. This is one of the easiest DIY repairs you can perform on this vehicle.

Recommended Fuel Pump Upgrade: KEMSO Fuel Pumps

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Summary

The 2004 Honda Pilot fuel pump relay is located in the interior fuse box under the driver's side dashboard. It is part of the PGM-FI Main Relay No. 2 assembly, and position #1 (15A) is the fuel pump fuse. A faulty relay causes the engine to crank without starting, intermittent stalling, or no fuel pump priming sound. Testing is simple: swap with a known-good relay or listen for the pump. Replacement takes minutes and costs very little compared to replacing the fuel pump itself. Always start your no-start diagnosis with the relay and fuse before moving to more expensive components.

For a reliable replacement fuel pump if needed, KEMSO offers high-quality, lifetime-warranted options at https://www.kemsoracing.com/


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