2004 Honda Odyssey Fuel Pump Relay Location & Replacement Guide

Finding the fuel pump relay in your 2004 Honda Odyssey is straightforward: it's located in the interior driver's side fuse box, specifically in position #17 (sometimes labeled as S7). This box is found under the dashboard near the driver's left leg.

Understanding the location and function of the fuel pump relay is crucial for diagnosing and resolving no-start or fuel pump issues common in the 2004 Honda Odyssey. When this relay fails, the vital electrical signal needed to activate the fuel pump and build pressure in the lines is interrupted. This guide provides the exact location, step-by-step access instructions, and essential safety practices.

The Critical Role of the Fuel Pump Relay

Every time you turn the key in your Odyssey, a sequence of events must occur precisely. One key step involves the Powertrain Control Module (PCM) recognizing the ignition position and signaling the fuel pump relay to energize. The relay acts as a heavy-duty electronic switch:

  • Low-Current Control: It receives a small signal from the PCM (computer).
  • High-Current Switch: Using that small signal, it connects high-current power from the battery directly to the fuel pump.
  • Pre-start Prime: When you first turn the key to "ON" (before starting), the relay activates for a few seconds, commanding the fuel pump to pressurize the fuel system.
  • Engine Running: Once the engine starts and the PCM detects engine rotation, it keeps the relay activated continuously to power the pump while driving.
  • Engine Shutdown: Turning the key off deactivates the relay, cutting power to the pump. A failed relay means the fuel pump receives no power, resulting in a cranking engine that never starts.

Pinpointing the Relay: Interior Driver's Fuse Box

Forget the engine compartment fuse box. Honda placed the vital primary under-dash interior fuse panel for the 2004 Odyssey inside the cabin:

  1. Position: Directly above the driver's left footwell, underneath the dashboard. Look towards the far left side near the door.
  2. Identification: This is a black plastic rectangular box mounted sideways near the door sill/kick panel area. It might have a removable plastic lid.

Accessing the Fuse Box Cover

Gaining access requires a few simple but necessary steps:

  1. Prepare the Area: Move the driver's seat fully rearward for maximum legroom. Park the Odyssey on a level surface and ensure the parking brake is firmly set.
  2. Locate the Lower Trim Panel: Identify the plastic trim panel directly above the driver's footwell area. This panel runs along the bottom edge of the dashboard and the side kick panel. The fuse box cover is part of this lower panel structure.
  3. Release the Cover:
    • Find the small plastic finger tab or slot usually located on the outboard edge (closest to the door) of the lower trim panel/fuse box cover.
    • Firmly pull this tab/slot directly towards you (outward, perpendicular to the dashboard). The cover should detach smoothly.
    • Some models might require gently pulling the cover downward near the edge closest to the seat. Pull firmly but carefully to avoid breaking clips.
  4. Remove Cover: Once all clips release, lower the cover fully and set it aside.

Identifying the Fuel Pump Relay (#17)

With the cover removed, you'll see the interior fuse box. Here's how to find the relay:

  1. Understand Layout: The box contains numerous fuses (smaller, often colorful plastic components) and likely several larger black cube-like components – these are the relays.
  2. Look for Labels: Carefully examine the fuse box cover you removed. The underside must have a printed diagram labeling every fuse and relay position with its number and corresponding function. Study this diagram closely.
  3. Find Position #17: Systematically scan the diagram for the position labeled "FUEL PUMP," "P/G," "PGM-FI," "FP," or "MAIN RELAY". Crucially, find the position labeled "17" or "S7". On the 2004 Odyssey, "17" is the standard position designation. "S7" is sometimes used interchangeably to refer to that slot position in Honda wiring references. Rely on the functional label ("FUEL PUMP") and position number "17" as your primary guide. If your cover diagram lists "S7" as the fuel pump relay, trust that.
  4. Match Location: Now look inside the physical fuse box itself. Identify the slot labeled #17 or S7. Verify it matches the position you found on the diagram. If your cover diagram uses "S7", look for that marking directly on the fuse box housing near the slot.
  5. Identify the Relay: The fuel pump relay is a standard black automotive relay, typically a cube shape roughly 1 inch wide and 1.5 inches long. It plugs directly into position #17/S7. It will likely be physically similar in appearance to other relays in the box. Its unique identity comes solely from its position.

Safely Removing the Fuel Pump Relay

Always prioritize safety before handling electrical components:

  1. Disconnect the Battery:
    • Turn the ignition OFF and remove the key. Open the hood.
    • Identify the NEGATIVE ( - ) battery terminal. It has a black cable attached.
    • Using the correct size wrench (usually 10mm), loosen the nut securing the terminal clamp.
    • Once loose, carefully lift the negative cable clamp straight up and off the battery terminal.
    • Isolate the cable end securely away from the battery terminal to prevent accidental contact. Covering the terminal with a clean cloth is an optional extra precaution. Wait a few minutes before proceeding.
  2. Extract the Relay: Firmly grasp the fuel pump relay at its plastic body. Pull it straight out from its socket in the fuse box. Do not rock it side-to-side. Use steady, even pressure. It should release relatively easily.

Testing the Fuel Pump Relay (Optional but Recommended)

Testing helps confirm failure. While physical swapping with an identical known-good relay is often faster, testing provides absolute certainty:

  1. Visual Inspection: Examine the relay's electrical pins for severe corrosion, bending, or burn marks. Inspect the plastic housing for cracks, melting, or distortion. Any significant damage indicates replacement is necessary.
  2. Bench Testing (Basic):
    • You will need a multimeter (set to continuity or ohms).
    • Identify the relay pin configuration: Two pins will be for the relay COIL (usually pins 85 & 86). Two pins will be the relay SWITCH contacts (usually pins 30 & 87). Find a diagram online for the specific relay number printed on the relay housing (e.g., "37932-SDA-A01", "RY-199", etc.).
    • Test Coil Resistance: Place multimeter probes on pins 85 & 86. Expect a reading typically between 50-120 ohms. An open circuit (infinite resistance) or a short (0 ohms) means a bad coil.
    • Test Switch Contacts: Place probes on pins 30 & 87. The meter should show an open circuit (no continuity). Apply 12 volts (from a small 12v power supply, battery, or using wires from your car battery) across the coil pins (85 & 86 - positive typically goes to pin 85 for Honda). You should hear and feel a distinct click. While keeping voltage applied to the coil, check pins 30 & 87 again. The meter should now show continuity (near 0 ohms). If it doesn't click or continuity doesn't change, the internal switch is faulty. Release the 12v power from the coil, pins 30 & 87 should return to open circuit.
  3. Simple Swap Test: The most practical test in the vehicle: Find another relay in the same under-dash fuse box that looks identical to the fuel pump relay (common candidates are the Blower Motor relay or Rear Defogger relay). Confirm it's not a critical one. Swap the fuel pump relay (from position #17/S7) with the identical relay you identified. Reconnect the battery negative cable. Turn the key to ON. Listen carefully:
    • If the pump now primes briefly (you'll hear a distinct humming sound from under the rear seats) when you insert the swapped relay, the original relay (#17) was faulty.
    • If no prime occurs, either the replacement relay is also bad (unlikely) or the problem lies elsewhere (fuse, pump itself, wiring, PCM issue). Note: Only perform this test briefly to listen for the prime. Do not attempt to start the engine with relays potentially in the wrong positions.

Reinstalling or Replacing the Fuel Pump Relay

  • If Testing Confirmed Relay Failure: Obtain an exact replacement relay. Match the Honda part number or standard relay number (e.g., HONDA Part Number: 37932-SDA-A01, or a standard equivalent like Bosch 0 332 019 129, Omron G8HN, etc.). Quality OEM or reputable aftermarket (Denso, Bosch, Hella) is recommended. Avoid unknown brands.
  • Installation: Ensure the battery remains disconnected. Take the new or known-good relay. Align its pins correctly with the socket in position #17/S7. Apply firm, straight pressure until it clicks securely into place. Do not force it.
  • Replace Fuse Box Cover: Snap the plastic lower trim panel/fuse box cover back into its original position. Ensure all clips engage correctly. You should feel and hear them snap securely. No gaps should exist around the cover.

Reconnecting the Battery and Testing

  1. Final Connection: Reconnect the NEGATIVE ( - ) battery cable. Tighten the terminal clamp nut securely.
  2. Initial System Test: Turn the ignition key to the "ON" (RUN) position, but do NOT start the engine. Immediately after turning the key to ON:
    • Listen: You should clearly hear the fuel pump hum for approximately 2 seconds as it primes the system. This sound typically comes from the rear, under the van near/under the second-row seats (where the fuel tank and pump assembly are located). This brief priming sound is your immediate confirmation that the relay is activating correctly. If you hear this sound, the relay replacement has addressed the electrical power issue.
  3. Engine Start Test: After confirming the prime sound, turn the key fully to the "START" position to crank the engine. The engine should start within a few seconds.

Troubleshooting If No Start Persists (Post-Relay Replacement)

If the pump primes (you hear the sound) but the engine still fails to start, the issue was not the relay or the power supply to the pump itself. Focus elsewhere:

  1. Confirm Fuel: Rule out the simple! Is there adequate fuel in the tank? Sounds obvious, but fuel gauge failures happen.
  2. Check the Fuel Pump Fuse: Locate the interior fuse box again. Using the diagram on the cover, find the fuse for the FUEL PUMP. It is typically Position #14 or S4 (a 15 Amp fuse). Remove it and inspect the metal element inside the clear plastic housing. Is it intact, or is the metal visibly broken/melted? Replace with an exact amperage fuse if blown. Note: A blown fuel pump fuse AFTER changing the relay could indicate a wiring short or a failing pump drawing excessive current.
  3. Listen for Fuel Pump Whine Under Van: If you didn't hear the prime earlier, try again with the ignition ON. Have a helper turn the key while you listen carefully near the fuel tank area. No sound at all strongly suggests no power is reaching the pump (check relay installation position again, fuse, wiring) or the pump itself is internally failed. A buzzing, straining, or whining sound instead of a normal smooth hum might indicate a weak or failing pump.
  4. Check Fuel Pressure: Lack of fuel pressure is the most common cause when pump power is confirmed. Requiring a fuel pressure gauge (screws into the Schrader valve on the fuel rail under the hood): Attach gauge. Turn key ON to prime. Check pressure reading against spec (typically 50-60 PSI for this engine). Low or no pressure after relay fix points to:
    • Faulty fuel pump (most likely).
    • Clogged fuel filter (integrated into the pump assembly on the 2004 Odyssey).
    • Severe obstruction in the fuel line.
    • Failed fuel pressure regulator.
    • Severe fuel leak bleeding off pressure.
  5. Ignition/Spark Related Issues: Problems with spark plugs, ignition coils, crankshaft position sensor, or other ignition components can also prevent starting. Requires specific diagnosis.
  6. Mechanical Engine Problems: Timing belt failure (though rare on this interference engine unless neglected), severe compression loss, etc. Listen for unusual cranking sounds.
  7. PCM Issues: Less common, but problems with the Powertrain Control Module itself or the circuits commanding the fuel pump relay could be the root cause. Requires professional diagnosis. Important Note: A failed fuel pump relay is statistically the most common single cause of a sudden no-start where the engine cranks normally but doesn't run on a 2004 Odyssey. Testing the prime sound immediately after relay replacement is the quickest functional confirmation.

Key Safety Precautions Throughout the Process

  • Battery Disconnect Mandatory: Always disconnect the NEGATIVE battery terminal first and reconnect it last. This prevents accidental short circuits that can damage fuses, relays, or wiring and pose a severe fire or injury risk. Isolate the cable end securely.
  • Minimize Static: Touch a grounded metal part of the car body (door striker, hood latch bracket) before handling relays or fuses to discharge static electricity which can damage sensitive electronics.
  • Avoid Metal Tools Near Fuse Box: Use plastic interior trim tools or your hands whenever possible near the fuse box terminals to prevent bridging contacts.
  • Use the Correct Relay: Ensure the replacement relay matches the original specifications exactly. Using an incorrect relay can cause malfunctions, damage, or fire.
  • Secure Loose Covers: Never drive with the fuse box cover or interior trim panels removed. Secure them correctly before operating the vehicle. Loose panels can interfere with pedals.
  • Fire Extinguisher: Keep one accessible nearby when working on automotive electrical systems. Be prepared.

By following this comprehensive guide, you now possess the precise location, detailed access procedures, testing methods, and replacement steps for the fuel pump relay in your 2004 Honda Odyssey. Prioritize safety, particularly concerning battery disconnection, and verify the repair with the critical system prime sound test. Addressing a faulty relay promptly restores reliable operation.

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