2002 7.3 Fuel Pump Relay Location: Exactly Where to Find & Diagnose It

The fuel pump relay for the 2002 Ford Super Duty equipped with the 7.3L Power Stroke diesel engine is located inside the engine compartment's main power distribution box. Specifically, it is found in socket position #301. This relay is critical for powering the engine's fuel pump and injector system when you turn the ignition key to the "Run" and "Start" positions. Knowing its precise location is essential for diagnosing crank-no-start conditions or fuel delivery problems.

Understanding the role and location of the fuel pump relay can save significant time and money when troubleshooting. Knowing where to look prevents unnecessary component replacements. This relay serves as the primary electrical switch controlled by the ignition switch, supplying battery power to the fuel pump and the critical Injector Drive Module (IDM). When you experience engine cranking but no start, a faulty fuel pump relay is a common suspect and one of the first items to check.

Locating the Under-Hood Power Distribution Box

The primary power distribution center for the 2002 7.3L Power Stroke resides in the engine compartment. Drivers standing outside the vehicle will find it easily.

  • Look for the large, black plastic box. This box sits securely on the driver's side (left side in Left-Hand Drive markets like North America) of the engine compartment. Its prominent size and black color make it noticeable. It lies relatively flat near the firewall area. If comparing positions, it sits behind the brake master cylinder/booster assembly and towards the driver's side fender from the engine block.
  • Identifying the box is straightforward. The top of the box features a molded plastic cover. This cover typically has clear labeling stating "Power Distribution Box" or similar wording. Removing this cover requires lifting a latch mechanism, usually located near the front of the box closest to the radiator. Lift the latch upwards to release the cover. Carefully lift the cover straight up to remove it. Place it safely aside where it cannot fall or be damaged.

Pinpointing Relay #301 Inside the Box

Once the power distribution box cover is removed, you'll see an organized array of large fuses (called maxi-fuses or cartridge fuses), smaller fuses (mini fuses), and several square or cube-shaped relays. Finding Relay #301 requires identifying the correct socket amongst these components.

  • Look directly at the inner surface of the box cover you just removed. Ford thoughtfully provides a detailed diagram of the entire fuse and relay layout inside this box. This diagram is usually embossed or printed on the underside of the cover. It clearly labels each fuse slot and relay socket with both an identifying number and its designated function.
  • Search the diagram for "301". The relays are typically labeled with numbers starting from 300 or so. Scan the diagram specifically for the number "301". You will see it clearly marked. Adjacent to the number "301", the diagram explicitly states the relay's function. Look for labels like "Fuel Pump", "Fuel Pump Relay", "PCM Power Relay", or "Fuel Injector Power Relay". These names refer to the component controlling power to the fuel pump and injector system. The function name confirms you are looking at the correct relay slot.
  • Locate relay socket #301 inside the box. Using the diagram as your guide, visually locate the socket labeled "301" within the power distribution box itself. The socket locations correspond directly to the map on the cover. Look for the small "301" molded into the plastic base of the socket. Position #301 is consistently situated within the power distribution box for this model year and engine.
  • Confirm with the function name. Double-check that the relay socket identified as #301 also corresponds to the fuel-related function described on the cover diagram. This dual confirmation eliminates any possible confusion.

Understanding Relay #301 (Fuel Pump/Injector Power Relay)

Relay #301 in the 2002 7.3L Power Stroke is not named arbitrarily. Its function is critical for engine operation, going beyond simply naming it a "fuel pump relay".

  • It controls high-amperage power. This relay acts as the main electrical switch that bridges the connection between the vehicle's powerful battery and the fuel system's electrical demands. The ignition key does not directly handle this large power load. Instead, turning the key sends a smaller signal that activates Relay #301.
  • When active, it powers key components. Upon receiving the signal from the ignition switch (via the PCM/IDM), Relay #301 "closes" its internal switch. This action allows a large current from Battery Positive Voltage to flow through the relay contacts. This large current simultaneously powers both the electric in-tank fuel pump and the high-pressure injector system managed by the Injector Drive Module (IDM). Engine operation requires both. Without this relay activating, neither system receives power, leading to a crank-no-start condition. Fuel pump operation is necessary to supply fuel to the engine compartment. Injector power is crucial for the injectors to fire properly. Loss of power here stalls the entire operation.
  • Alternative names. Due to its role, this relay might be listed under different names in parts databases or diagrams: "PCM Power Relay" (since power flows through it to components controlled by the PCM/IDM), "Fuel Injector Power Relay", or "Fuel Injection Relay". Despite different names, Relay #301 is consistently referenced by its position number (#301) and its core function controlling injector and pump power.

Visually Identifying the Fuel Pump Relay

Relay #301 is a standard International Standards Organization (ISO) mini relay, commonly used throughout automotive applications.

  • It is a small, square plastic cube. Dimensions are typically around 1 inch (25mm) wide, 1 inch (25mm) deep, and slightly taller. It has a mostly opaque white or black plastic case. The casing is sturdy plastic.
  • It plugs into a socket with multiple slots. The bottom of the relay has several metal pins that insert into corresponding slots in the socket (#301). The relay is not screwed in; it clips into place via its pins and socket design.
  • Look for the labeling on the relay. While physical characteristics identify it, finding "301" molded into the plastic base of the socket underneath it is the absolute confirmation. Some relays themselves might have an internal part number printed on them (like F5TZ-14N192-AA or F65Z-14B192-AA), but the socket position (#301) is the primary identifier for location and function.

How To Remove and Inspect the Relay (Step-by-Step)

Before attempting removal, ensure the ignition key is in the OFF position and removed from the ignition cylinder for safety. Avoid potential electrical shorts or unexpected starting.

  1. Locate Relay Socket #301: Confirm you have found socket #301 inside the power distribution box using the cover diagram and molded numbering.
  2. Grasp the Relay Firmly: Place your thumb on top of the relay. Position your fingers underneath it, around the sides near the base. A standard relay removal requires a simple pulling action.
  3. Pull Straight Up Steadily: Apply firm, even upward pressure. Pull directly vertically along the relay's axis. Avoid excessive wiggling or twisting at an angle, as this could potentially damage the relay pins or the socket terminals. As you pull, you should feel the relay release its friction fit within the socket. The relay should slide out relatively smoothly if pins are not corroded. It should come out as a single unit.
  4. Inspect the Relay: Once removed, visually inspect the relay. Check for obvious signs of damage: excessive heat discoloration (especially melting plastic around terminals), cracks in the plastic casing, corrosion on the metal pins, or signs of burning. Light surface corrosion might be cleanable; significant damage requires replacement.
  5. Inspect the Socket: Briefly look into socket #301. Check for signs of corrosion on the metal terminals, bent pins, or any debris blocking connections. Damaged sockets require professional repair.

Testing the Fuel Pump Relay (Simple Swap Test)

The quickest and most reliable way to test Relay #301 if you suspect it has failed is the swap test. This method leverages other identical relays present in the power distribution box.

  1. Identify a Known Good, Identical Relay: Locate another relay in the power distribution box that matches Relay #301 physically (same size/shape). Commonly recommended donor sockets include the #302 (A/C Compressor Clutch Relay), #303 (Blower Motor Relay), #304 (Trailer Tow Backup Lamp Relay), or #305 (Trailer Tow Park Lamp Relay). Refer to the diagram on the power distribution box cover to find these positions.
  2. Swap the Relays: Carefully remove the suspect Relay #301 from its socket. Carefully remove the relay chosen as the donor from its known working socket. Place Relay #301 (the suspect unit) into the donor relay socket you just emptied. Place the donor relay (which was working correctly) into the socket #301 position previously occupied by the suspect relay.
  3. Test Operation: Ensure the ignition key is OFF initially. Turn the ignition key to the "RUN" position (but do not crank the engine). Listen carefully near the fuel tank or under the hood near the fuel bowl. A functioning relay should click loudly within a second or two after turning the key to RUN, and you should hear the fuel pump run for 1-3 seconds (a distinct buzzing/humming sound). If equipped, the "Wait to Start" light should also illuminate normally. If the problem symptom (crank-no-start) was present, try to start the engine.
  4. Interpret Results:
    • If the fuel pump runs normally, "Wait to Start" light comes on, and the engine starts after swapping relays: This strongly indicates the original Relay #301 (now located in the donor socket) is faulty and caused the problem. Replace it.
    • If the fuel pump still DOES NOT run and/or the engine still doesn't start, BUT the relay in the donor socket now clicks: This suggests Relay #301's socket is receiving the correct activation signal from the ignition, but the donor relay isn't functioning in socket #301 OR there's another problem besides the relay itself (like a blown fuse, fuel pump failure, or wiring issue). It's less conclusive about the relay.
    • If the relay now in the donor socket does NOT click when the key is turned to RUN: This points to a problem elsewhere in the activation circuit (ignition switch fuse, wiring, PCM/IDM fault), not the relay itself. Further diagnosis is needed.

Related Components to Check (Fuses)

When troubleshooting issues potentially linked to Relay #301, always check the associated high-amperage fuses first. They are more likely to blow than the relay itself and cause identical symptoms (crank-no-start).

  • Fuse #19 (30A): Protects the coil side (activation circuit) of Relay #301. This circuit triggers the relay to switch on. A blown Fuse #19 prevents the relay from being activated at all. It is usually a yellow 30A mini fuse located within the power distribution box. Check the cover diagram to locate fuse position #19 specifically.
  • Fuse #23 (30A): Protects the load side (output circuit) of Relay #301. This carries the high current powering the fuel pump and injector system. A blown Fuse #23 cuts power downstream even if the relay clicks. It is typically a yellow 30A mini fuse located within the same power distribution box. Check the cover diagram to locate fuse position #23 specifically.
  • Fuse #22 (30A): Protects the fuse box itself where these components reside. Less common to fail for this specific symptom, but possible. Confirm via the diagram. Often a yellow 30A mini fuse.

To check fuses, remove them visually. Look for a broken metal element inside the clear plastic housing. A continuity tester or multimeter is the most reliable method to definitively test for a blown fuse, especially if the break isn't visible.

Replacing a Faulty Fuel Pump Relay

If testing confirms Relay #301 is faulty, replacement is simple. Ensure the ignition is OFF.

  1. Procure the Correct Replacement: Obtain a new ISO mini relay matching Ford's specification. Common Ford OEM part numbers include F5TZ-14N192-AA or F65Z-14B192-AA. Standard automotive ISO mini relays available at any auto parts store (like Bosch, Tyco, Omron, Denso) are suitable equivalents (ensure it matches relay specs: typically 12V, 20A/30A contacts, ISO Form A). Double-check relay compatibility with store staff if unsure.
  2. Remove the Old Relay: Remove the old relay as described above (pull straight out from socket #301).
  3. Insert the New Relay: Orient the new relay correctly over socket #301. The socket may be keyed (have slots or shapes preventing incorrect insertion). Match the relay pin configuration to the socket slots. Press the relay firmly straight down into the socket until it clicks and seats fully. You should feel it snap securely into place.
  4. Test Operation: Turn the ignition key to the "RUN" position. Listen for the relay clicking and the fuel pump priming (1-3 second buzz/hum). The "Wait to Start" light should illuminate. If the issue was just the relay, the engine should start normally.

Symptoms of a Failing Fuel Pump Relay

Several symptoms can indicate a problem with Relay #301 or its circuits (fuses, wiring):

  • Crank-No-Start: The engine cranks over healthily but absolutely fails to fire or start. This is the most common and classic symptom. No combustion occurs.
  • No Fuel Pump Prime: When turning the key to "RUN" (before cranking), the distinct sound of the fuel pump running for 1-3 seconds is absent. The engine area remains silent after turning the key.
  • No "Wait to Start" Light: The Glow Plug/"Wait to Start" indicator light on the dashboard fails to illuminate when the ignition key is turned to "RUN". The IDM relies on the same power circuit activated by Relay #301.
  • Engine Stall After Running: The engine unexpectedly dies while driving or idling, potentially indicating an intermittent relay failure. Vehicle loses power suddenly.
  • Intermittent Starting Problems: The vehicle occasionally starts normally, but other times exhibits crank-no-start, potentially due to a failing relay making partial contact or working only sometimes.
  • Absence of Relay Click: The distinct audible click that should occur within a second of turning the key to "RUN" is missing. Lack of the click suggests the relay isn't being commanded to activate or is seized internally.

When Location Knowledge is Essential

Knowing the precise location of Relay #301 (#301 in the Under-Hood Power Distribution Box) is crucial in several common scenarios:

  1. Troubleshooting Crank-No-Start: This is the primary diagnostic step. Quickly checking/swapping this relay (and associated fuses #19 and #23) can confirm or rule out a common and easily fixed cause. Getting stuck without the ability to start requires fast action.
  2. Replacing a Faulty Relay: When diagnosis confirms the relay itself is bad, knowing exactly where to plug in the replacement prevents delays. Mechanics and owners save valuable time.
  3. Electrical System Maintenance: Inspecting the relay and socket contacts for corrosion or damage during routine service. Preventative checks avoid future breakdowns. Connections exposed to heat and moisture deteriorate over time.
  4. Installing Accessories: Understanding the main power center is helpful when adding auxiliary electrical components, though caution is needed to avoid overloading circuits. Relays control heavy electrical loads.

Additional Considerations

  • Injector Drive Module (IDM): The IDM controls the fuel injectors and relies heavily on the power provided via Relay #301. A lack of power to the IDM causes crank-no-start and no "Wait to Start" light, mimicking relay failure. While less common than relay failure, IDM problems require more involved diagnosis and repair. The IDM typically resides inside the cab under the dashboard.
  • Wiring Issues: Corrosion, breaks, or shorts in the wiring harness connecting the battery to Relay #301, Relay #301 to the fuel pump/IDM, or the ignition/PCM to Relay #301 can cause identical symptoms. Visual inspection along wiring runs and connectors is necessary if the relay and fuses test good.
  • Ignition Switch Failure: If the ignition switch fails to send the "Run" signal needed to activate Relay #301, symptoms appear. Check other systems powered in the "Run" position for function.
  • PCM/IDM Signal Failure: While less likely than the relay, fuse, or wiring, a failure within the PCM or IDM could prevent the activation signal from being sent to Relay #301. Professional diagnostics are usually required to confirm this. Specialized scanner tools access computer codes.
  • Fuel Pump Failure: Remember, a bad fuel pump itself will cause no pump prime sound and crank-no-start, even if Relay #301 and its fuses are functioning perfectly. Testing the pump requires verifying voltage at the pump connector or listening to it directly. Knowing pump location near the tank helps.

Conclusion:

The precise location of the fuel pump relay is essential knowledge for 2002 Ford Super Duty 7.3L Power Stroke owners. Remember the core fact: The fuel pump relay for a 2002 7.3L Power Stroke is Relay #301 inside the under-hood power distribution box. Keep the box cover diagram handy to identify the position. Always start with fuse checks (#19 and #23) and the simple relay swap test when diagnosing crank-no-start issues. Understanding this critical component's location and function empowers you to tackle common problems efficiently, often avoiding unnecessary towing or expensive shop diagnostics. For issues beyond a straightforward relay or fuse replacement, consult repair manuals or seek professional assistance for complex electrical diagnostics on the vehicle system. Knowing Relay #301's location is your key first step.

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