1991 Honda Civic Fuel Pump Relay Location: Your Essential Guide

Finding the fuel pump relay in your 1991 Honda Civic is straightforward: it's located inside the main under-hood fuse and relay box, positioned near the battery on the driver's side of the engine compartment. Specifically, look for a small, typically black, cube-shaped relay plugged into a socket within this box.

Knowing the exact location of the fuel pump relay is crucial for diagnosing and fixing a common problem that can leave your Civic stranded. If your car cranks but won't start, and you don't hear the brief humming sound of the fuel pump priming when you turn the key to the "ON" position (before cranking), a faulty fuel pump relay is a prime suspect. Locating it is the first step in testing or replacing it.

Detailed Location Inside the Under-Hood Fuse/Relay Box

  1. Open the Hood: Securely prop open the hood of your 1991 Civic.
  2. Locate the Fuse/Relay Box: Walk to the driver's side of the engine bay. Look for a rectangular, usually black, plastic box situated near the battery. This is the primary fuse and relay box.
  3. Open the Box Lid: The box has a lid secured by clips. Carefully unclip and lift the lid off. Set it aside safely.
  4. Identify the Relay: Inside the box, you'll see an array of fuses (small, often colored plastic components with metal strips visible on top) and several larger, cube-shaped components plugged into sockets – these are the relays.
  5. Finding the Correct Relay: The fuel pump relay in the 1991 Civic is often grouped with other important relays. Look for a relay that matches the description printed on the underside of the fuse box lid. The lid typically has a detailed diagram labeling each fuse and relay position. Crucially, locate the relay labeled "FUEL PUMP" or "FP." This is your target.
    • Visual Identification: The fuel pump relay itself is a small, square or slightly rectangular, black plastic cube, usually about 1 to 1.5 inches per side. It has several electrical prongs (terminals) protruding from its bottom that plug into the socket. The top might have a faint circuit diagram or just be plain.
    • Common Mistake: Be careful not to confuse it with the very similar looking PGM-FI Main Relay (often labeled "PGM-FI" or "MAIN"), which is also located in this same box and is a very common failure point on Hondas of this era. The PGM-FI relay actually powers the fuel pump relay among other things. Double-check the label on the lid or the relay socket itself (if marked) to ensure you have the correct one labeled for the fuel pump.

Why Knowing This Location Matters

The fuel pump relay acts as a switch controlled by the engine computer (ECU). When you turn the key to "ON," the ECU briefly energizes this relay. The relay then closes its internal contacts, sending full battery power to the electric fuel pump located inside the fuel tank. This allows the pump to pressurize the fuel system for a few seconds. When you crank the engine, the ECU keeps the relay energized to provide continuous power to the pump while the engine runs.

If this relay fails, it cannot send power to the fuel pump. The result is a car that cranks but absolutely will not start because no fuel is being delivered to the engine. Symptoms mirror a completely dead fuel pump. Locating the relay allows you to:

  1. Test It: You can perform simple tests like swapping it with an identical, less critical relay (like the horn relay, if the same type) to see if the problem resolves. You can also test it for power and proper switching function using a multimeter.
  2. Inspect It: Sometimes, visual inspection can reveal burnt or melted plastic, indicating failure.
  3. Replace It: Replacing a faulty relay is generally inexpensive and significantly easier and cheaper than replacing the fuel pump itself, which requires dropping the fuel tank.

Safety Precautions Before Handling

  • Disconnect the Battery: Always disconnect the negative (-) terminal of the battery before touching any relays or fuses. This prevents accidental short circuits, sparks, or electrical shock. Wait a few minutes after disconnecting before proceeding.
  • Work on a Cool Engine: Ensure the engine is completely cool to avoid burns.
  • Use Proper Tools: Needle-nose pliers can sometimes help gently wiggle a stuck relay out, but avoid excessive force. Fingers are usually sufficient.

Removing the Fuel Pump Relay

Once you've positively identified the correct fuel pump relay:

  1. Grasp Firmly: Place your fingers securely around the body of the relay.
  2. Pull Straight Up: Apply steady, even pressure straight upwards. Do not twist or rock it excessively, as this can damage the socket or the relay terminals. It should pull out smoothly.
  3. Inspect Socket: With the relay removed, take a quick look at the socket. Check for any signs of corrosion, bent pins, or melted plastic. These issues would need addressing beyond just relay replacement.

Replacing the Fuel Pump Relay

  1. Obtain Correct Replacement: Ensure you get a relay specified for the 1991 Civic fuel pump circuit. Using an incorrect relay can cause malfunctions or damage. The part number is often printed on the relay itself (e.g., Honda part numbers like 39400-SH3-XXX are common, but aftermarket equivalents like Standard Motors RY-268 are widely available). Cross-reference is key.
  2. Orient Correctly: Look at the relay and the socket. They have a specific orientation. The relay prongs and the socket holes are shaped or arranged so it only fits one way. Align the relay correctly over the socket.
  3. Press Firmly Down: Apply firm, even pressure straight down onto the relay until it seats fully into the socket. You should feel or hear a distinct click when it's properly seated. Ensure it's secure and level.

Troubleshooting Tips

  • Swap Test: As mentioned, swapping the suspected fuel pump relay with another identical relay in the box (like the horn relay) is a quick diagnostic test. If the horn stops working and the car starts (or the fuel pump primes), you've confirmed the original fuel pump relay is bad. Remember to swap them back and replace the faulty one.
  • Listen for the Pump: Before and after swapping, have a helper turn the key to "ON" (not start) while you listen near the fuel tank (rear seat area or under the car). You should hear a 2-3 second whirring/humming noise if the pump is getting power. No sound points strongly to a relay (or fuse, or pump) issue.
  • Check the Fuse: While you're in the fuse box, locate the fuse associated with the fuel pump circuit (often 15 Amp, labeled "FP" or "FUEL PUMP" on the lid diagram). Visually inspect it or test it with a multimeter to ensure it's not blown. A blown fuse can cause the same symptoms as a bad relay, but often indicates a deeper electrical problem that caused the fuse to blow.

Conclusion

The fuel pump relay in your 1991 Honda Civic resides inside the main under-hood fuse and relay box, situated near the battery on the driver's side. Identifying it requires opening the box lid and locating the relay specifically labeled "FUEL PUMP" or "FP" on the diagram, differentiating it from the similar PGM-FI Main Relay. Knowing this location empowers you to test, inspect, and replace this critical component, often resolving frustrating no-start conditions quickly and economically. Always prioritize safety by disconnecting the battery before handling any electrical components. With this guide, you can confidently locate and address issues with your 1991 Civic's fuel pump relay.

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