The EXACT 1991 Honda Civic Fuel Pump Relay Location (And How To Fix It)

Stop searching – the fuel pump relay in your 1991 Honda Civic is located inside the driver's side under-dash relay box. Specifically, it sits in the position labeled "B" (typically the second position from the left in the bottom row of the box). Finding it requires removal of the driver's side lower dash panel.

A failed fuel pump relay is one of the most common reasons a 1991 Honda Civic won't start. If you turn the key and hear only silence from the fuel tank area near the rear seats, or the engine cranks but refuses to start, this small, crucial relay is very likely the culprit. Pinpointing its exact location quickly is essential for diagnosing and solving the problem.

Precise Location Details: Finding Relay Box & Position "B"

  1. Driver's Side Footwell: Sit in the driver's seat. Look towards the area where your knees naturally rest below the steering column. You'll see a large plastic panel that curves upward towards the bottom of the dashboard and wraps slightly to the left (towards the door).
  2. Lower Dash Panel Removal: This panel is held in place by multiple metal clips or screws (usually Phillips head). Carefully locate and remove all fasteners. The top and outer edges of the panel are hooked behind the dashboard trim above it. Once fasteners are removed, firmly grasp the panel at its upper corners near the dashboard and pull it straight back and slightly down towards the driver's seat. Expect some resistance as the clips release. Be gentle but firm; avoid forcing it.
  3. Locate the Relay Box: With the panel removed, you'll see various components. Look for a rectangular, often slightly grimy, black plastic box fixed to the metal structure of the dash frame. This is the primary under-dash relay and fuse box. It will have multiple relays plugged into sockets on its front face and possibly some larger fuses.
  4. Identify Position "B": Examine the front face of the relay box closely. You should find small labels molded or printed directly onto the plastic near each relay socket. Look specifically for the socket marked "B". This is the Fuel Pump Relay socket.
  5. The Relay Itself: The relay plugged into socket "B" is the fuel pump relay. It will be a small, rectangular, often dark gray, black, or tan plastic cube approximately 1 inch by 1 inch by 1.25 inches, with multiple electrical terminals protruding from the bottom that plug into the socket. It may have writing or numbers on it (like "Honda," a part number, or specs like "12V 20A").
  6. Visual Confirmation: The relay box typically has 5-6 relay positions. Position "B" is consistently designated for the fuel pump relay in 1988-1991 Honda Civics (4th generation, 'EF' chassis).

Why the Fuel Pump Relay Matters (And Why It Fails)

  • Its Critical Job: When you turn the ignition key to the "ON" (Run) position, the Powertrain Control Module (PCM, or ECU) sends a small signal current to the fuel pump relay. This signal energizes an electromagnet inside the relay, causing it to physically click closed an internal switch. Closing this switch completes the high-current circuit from the main fuse box under the hood, delivering vital battery power all the way to the electric fuel pump located inside the fuel tank. The pump then pressurizes the fuel lines for engine starting and operation.
  • Symptoms of Failure: A faulty relay manifests dramatically:
    • Complete Non-Start: The most common symptom. The engine cranks normally (starter works), but doesn't fire. You hear NO faint buzzing sound from the rear seat/fuel tank area when the key is turned to "ON."
    • Intermittent Failure: You might experience occasional hesitation, stalling, or failure to start after the car has been running and is warm ("heat soak"). The relay partially works but fails unpredictably when its internal contacts get hot.
    • Silent Fuel Pump: No sound from the pump within 1-2 seconds of turning the key to "ON" is a strong indicator of relay failure, a blown fuel pump fuse, or a dead fuel pump itself.
  • Common Failure Causes:
    • Aged Internal Contacts: This is the primary cause. After decades of use, the thin metal contacts inside the relay become burnt, pitted, or oxidized from arcing as they open and close millions of times. This prevents the high-current connection needed for the fuel pump.
    • Heat Damage: The relay's location in the confined, often hot space under the dash subjects it to significant heat cycles over years, accelerating internal wear and degrading the plastic housing and solder joints.
    • Corroded Terminals: The metal terminals where the relay plugs into the socket can become corroded over time, leading to poor electrical connections and increased resistance (voltage drop).
    • Fatigued Solder Joints: Manufacturing solder joints inside the relay can crack or fatigue with age, vibration, and heat, interrupting the circuit.

Diagnosing the Fuel Pump Relay: Simple Tests You Can Do

Before assuming the relay is dead, it's crucial to rule out other causes like a blown fuel pump fuse or a completely failed fuel pump.

  1. Listen for the Fuel Pump (Basic Check): Have an assistant turn the ignition key firmly to the "ON" (RUN) position (but do not crank the starter). Put your ear near the fuel tank access panel (usually under the rear seat bottom cushion) or listen carefully at the fuel filler neck. You should hear a distinct, medium-pitched buzzing/whirring sound for about 2 seconds as the pump primes the system. No sound here points directly towards the fuse, relay, or pump.
  2. Check the Fuel Pump Fuse (Protection First): Locate the under-hood main fuse/relay box (usually near the battery). Find the fuse labeled "F/PUMP," "FUEL PUMP," or "FI/ECU" (refer to your owner's manual or the fuse box diagram sticker). Carefully pull it out and visually inspect the thin metal strip inside. If the strip is visibly melted or broken, replace the fuse with one of the correct amperage rating (likely 15A). If a new fuse blows immediately, you have a significant short circuit downstream requiring professional diagnosis. Note: Fixing a blown fuse doesn't solve the root cause; it merely addresses the symptom. A blown fuse could be caused by a failing relay creating excessive current draw, or a failing pump, or damaged wiring.
  3. The Fuel Pump Relay "Click" Test: While the relay is plugged in under the dash, have your assistant turn the ignition key to "ON." Place your fingers on the fuel pump relay housing. You should feel and hear a distinct, solid CLICK within a second of turning the key. No click strongly suggests a problem with the relay or the signal circuit controlling it (less common than the relay itself failing).
  4. The Fuel Pump Relay Bypass/Substitution Test (Most Reliable Check):
    • Option A (Swap with an Identical Relay): Locate another relay in the under-dash box (or under-hood box) that has the EXACT same part number and socket terminal layout as the one in position B. Common identical relays in Civics include the horn relay or sometimes the fan main relay (check the molded number on the relay housing). WARNING: Only swap relays with identical part numbers. Swapping a different relay can cause damage.
    • Option B (Jumper Test - Exercise Extreme Caution):
      1. Unplug the fuel pump relay from socket "B".
      2. Examine the exposed socket. The terminals are numbered. You need to jumper between Terminal #1 and Terminal #2 in the socket itself. (Terminal #1: Should correspond to the Black/Yellow wire - Battery Power Always Hot. Terminal #2: Should correspond to the Green/White wire - Power to Fuel Pump). CRITICAL: Confirm these wire colors match using a flashlight or test light. DO NOT rely solely on position; wire colors are definitive.
      3. Use a heavy-gauge jumper wire or a specific relay socket bypass/jumper tool rated for at least 10-20 amps (a simple paperclip is insufficient and dangerous – it will overheat). Connect one end securely to the cavity for Terminal #1 (Black/Yellow wire) and the other end securely to the cavity for Terminal #2 (Green/White wire). Ensure no contact is made with other terminals or metal dash structures.
      4. Safety First: Have a fire extinguisher readily available. This bypasses all control circuits, sending power directly to the fuel pump.
      5. Perform the Test: Turn the ignition key to the "ON" position (do not crank yet). If your fuel pump is functional, you should hear the pump running continuously (a loud buzzing/whirring from the rear). If you now attempt to start the engine, it should fire and run (but be prepared to turn the key off immediately as the pump will run constantly). If you hear the pump run and the engine starts during this bypass, THE FUEL PUMP RELAY IS FAULTY and must be replaced. If the pump still doesn't run during the bypass, the problem lies elsewhere (fuse - though you should have checked this first, pump, or wiring). Remove the jumper wire immediately after testing.

Replacing the Faulty Fuel Pump Relay (A Simple Fix)

  1. Source the Correct Relay:
    • Honda OEM: Provides the best quality and fit. Ask for the fuel pump relay for your specific 1991 Civic (VIN helps). Part numbers like 39794-SP0-A01 or supersessions are common, but rely on dealer confirmation.
    • Quality Aftermarket Brands: Standard Motor Products RY-115, Beck/Arnley 201-1630, or NAPA Echlin AR112, etc. Stick with major brands sold at reputable auto parts stores. Avoid the absolute cheapest options.
    • Bring the Old One: Taking your faulty relay for direct visual comparison is the best way to ensure a perfect match. Confirm the number of pins and terminal layout alignment.
  2. Removal & Installation: With the ignition OFF, simply grasp the old relay firmly and pull it straight out of socket "B". Align the pins of the brand new relay precisely with the socket terminals (critical: check for any bent pins!) and push it firmly and evenly straight in until it seats fully. You should hear/feel it click into place.

Beyond the Relay: Other Possible Causes of No Fuel Pump Operation

If replacing the relay solves the problem, you're done! If not, the issue lies deeper:

  1. Faulty Fuel Pump: The pump motor itself can seize or burn out. Diagnosed by verifying power (Green/White wire) and ground at the fuel pump connector near the tank. Requires dropping the fuel tank or accessing the pump through the rear seat/trunk floor panel. Replacement is labor-intensive. Test thoroughly first!
  2. Severe Wiring Problems:
    • Damaged Power Wire (Green/White): Cuts, chafing, corrosion anywhere from the under-dash relay socket to the fuel pump connector.
    • Damaged Ground Wire (Black): A bad ground connection for the fuel pump is incredibly common in 30+ year old Civics. The main fuel pump ground point (often designated G401) is notoriously problematic, located on the body panel near the EGR valve under the hood, passenger side firewall area. Locate this point (consult service manual wiring diagram for exact location), unbolt, clean the metal ring terminal and body surface down to bare metal, and securely reattach. Ground faults are a frequent hidden cause.
    • Damaged Connectors: Inspect large multi-pin connectors in the engine compartment and under the car. C305 (often near the passenger side strut tower) carries power to the rear harness and is prone to corrosion or terminal fatigue causing the Green/White wire to disconnect.
  3. Faulty Main Relay: Located under the driver's dash (often a larger relay in position "A"), it powers the ECU and injectors. A failed main relay typically causes a complete no-spark condition AND no fuel pump operation. Symptoms include the Check Engine Light (CEL) not illuminating when turning the key to "ON". This is the second-most common relay failure in older Civics.
  4. ECU/PCM Failure: Very rare compared to relay issues, but possible. Symptoms usually extend beyond just no fuel pump.

Preventive Maintenance and Tips for Longevity

  • Replace Proactively: If your car is exhibiting occasional hesitation or you simply never want to get stranded, consider replacing both the fuel pump relay and the main relay (position "A") preventively. Use Honda OEM or high-quality brands.
  • Clean Connections: When replacing the relay, briefly inspect the socket terminals for visible corrosion or bending. Use electrical contact cleaner spray on a small brush to gently clean them before plugging in the new relay.
  • Address Known Ground Issues: Clean and resecure the fuel pump ground point G401 under the hood before it causes problems. This is a high-impact, low-cost maintenance task.

Conclusion: Pinpointing Relay "B" is the First Step

When your 1991 Honda Civic cranks but refuses to start, suspect fuel delivery problems. The fuel pump relay located in socket "B" of the driver's under-dash relay box is frequently the cause. Finding it involves removing the lower driver's dash panel and identifying the correct socket. By learning its location and how to test it (especially the safe but definitive bypass method), you can quickly diagnose the most common failure point. Replace a faulty relay with a quality unit and secure that troublesome G401 ground connection under the hood to ensure many more reliable miles from your trusty Civic. Remember, start simple – that small relay in position "B" holds the key to getting your car back on the road.

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