1992 Dodge D150 Fuel Pump Relay: Essential Guide for Diagnosis & Replacement

Introduction: The Core Issue
A failing or failed fuel pump relay in your 1992 Dodge D150 can prevent the truck from starting or cause sudden stalling. This small, vital electrical component acts as a switch, controlling power to the electric fuel pump located inside the fuel tank. When it malfunctions, the fuel pump doesn't receive the necessary power to operate, starving the engine of fuel. Recognizing the symptoms and knowing how to diagnose, locate, and replace the relay is critical for getting your D150 back on the road reliably. This guide covers everything you need to know.

Understanding the Fuel Pump Relay's Role
The fuel pump relay solves a fundamental electrical challenge. The fuel pump requires significant electrical current (amperage) to run. If this high current traveled directly through the ignition switch and dashboard wiring, it would necessitate very heavy, expensive wiring throughout the truck and would quickly wear out the ignition switch. The relay solves this. A small, low-current signal from the ignition switch (or the Powertrain Control Module - PCM) activates an electromagnet within the relay. This magnet pulls internal contacts together, completing a separate high-current circuit that delivers power directly from the battery (fused) to the fuel pump. Essentially, it allows a small switch (the ignition key) to safely control a large electrical load (the fuel pump). The relay is crucial for both starting and maintaining engine operation.

Why the 1992 D150 Relay is Prone to Issues
Age is the primary factor. Over nearly three decades, the relay's internal components degrade. The electromagnet coil can weaken or break. The electrical contacts inside, which switch the high current, can become pitted, burned, corroded, or simply stick open or closed due to heat cycles and arcing. Exposure to engine bay temperature extremes and moisture accelerates this wear. While generally reliable when new, any electromechanical device like a relay will eventually fail after this long. Replacing an original 1992 relay is a common and necessary maintenance task.

Clear Symptoms of a Failing or Failed Relay
Symptoms related to the fuel pump relay are distinct because they directly affect fuel delivery:

  • Engine Cranks But Won't Start: The most common symptom. The starter engages and turns the engine over normally, but it never "catches" and runs because no fuel is being delivered to the engine.
  • Sudden Engine Stalling While Driving: A relay that works intermittently or fails while driving will instantly cut power to the fuel pump. The engine will suddenly die as if the ignition was turned off, often without warning.
  • No Fuel Pump Prime Sound: When you turn the ignition key to the "ON" position (before cranking), you should hear the fuel pump run for 1-2 seconds to pressurize the fuel system. If you consistently hear nothing from the rear of the truck when turning the key to "ON," the pump isn't getting power. (Note: Listen near the fuel tank area.)
  • Intermittent Starting Problems: A relay on the verge of failing might work sometimes and not others. You might experience difficulty starting the truck occasionally, or it might start after several crank attempts.
  • Absence of Power at the Fuel Pump: Confirmed via testing (covered later). If the pump has no power (and is confirmed functional or replaced), the relay is a prime suspect.

Locating the Relay on Your 1992 D150
The fuel pump relay in the 1992 Dodge D150 is found under the hood in the Power Distribution Center (PDC). This is a large, usually black plastic box located on the driver's side inner fender, near the battery and brake master cylinder.

  1. Open the Hood: Secure the hood prop.
  2. Identify the PDC Lid: The PDC cover has a diagram printed on its top surface showing the layout of fuses and relays inside. Look for this diagram.
  3. Find the Fuel Pump Relay Designation: On the PDC lid diagram, locate the relay labeled "Fuel Pump," "FP," "Fuel," or "Fuel/Auto Shutdown (ASD)". In many 1992 Rams, it was labeled as the "Auto Shutdown (ASD) Relay." This single relay often controls power to both the fuel pump and the ignition coil/injectors. Its failure impacts both fuel and ignition. Crucially, the label is your primary guide.
  4. Open the PDC: Unclip and remove the PDC lid.
  5. Identify the Relay Position: Match the diagram's location to the sockets inside the PDC box. Identify the socket corresponding to the Fuel Pump or ASD relay. The relay itself is a small cube-shaped component with electrical terminals on the bottom and sometimes wire colors entering it. Common Wire Colors on the relay (for reference, but diagram is key): Heavy gauge wires (power in/power out) are often Orange (or Dark Blue) and Dark Green. Control wires are smaller gauge Red or Tan with Dark Blue stripe, and another (ground control) might be Black.

Confirming Relay Failure: Diagnosis Before Replacement
Never replace parts blindly. Diagnosis is key to avoid unnecessary expense and ensure the repair is effective:

  1. Listen for the Fuel Pump: Turn the ignition key to "ON" (don't crank). Listen carefully near the fuel tank (rear of the truck) for a distinct buzzing or whirring sound lasting 1-2 seconds. No sound? Proceed to step 2. Sound heard? The relay and pump circuit are working at that moment; the problem is likely elsewhere (but intermittent relay failure is still possible).
  2. Visual Check the PDC: Look inside the PDC. Are any fuses blown? Specifically, check the main fuse feeding the relay (usually a large 20A, 30A, or 40A fuse listed on the lid diagram, often labeled "Fuel Pump," "PCM," "Auto Shutdown," or similar). Also, inspect the relay itself for obvious damage, corrosion, or overheating (melting plastic, discoloration). If the fuse is blown, replacing it is the first step, but its blowing indicates an underlying problem (like a failing pump or short).
  3. Swap with an Identical Relay (Best Test): The PDC contains multiple relays of the same type. Common identical relays include the horn relay, A/C clutch relay, or headlight relay (check diagram). Power down the system by disconnecting the negative battery cable. Pull out the suspected fuel pump relay and pull out another relay confirmed to be the exact same type from a non-essential circuit (like the horn). Install the known good relay (from the horn circuit, for example) into the fuel pump relay socket. Reconnect the battery. Turn the ignition to "ON" and listen for the fuel pump prime sound. If the pump now primes, the original relay is faulty. This is the most reliable method for a novice. Return the swapped relay to its original position once testing is complete.
  4. Test Relay Control Signal: Requires a multimeter or test light.
    • Identify the relay control circuit terminals using the PDC lid diagram or a repair manual. One should have battery voltage (12V+) with the key ON (typically labeled "IGN" or feed from PCM). The other is the control ground path, which the PCM momentarily activates during the prime cycle and maintains while running.
    • With key ON, check for power at the designated ignition-switched control terminal. If no power, trace back to fuse or ignition switch.
    • Check the PCM ground control terminal. It should show battery voltage when PCM is NOT activating it. When the PCM grounds it (during the prime cycle), voltage should drop near 0V. This requires timing and/or an assistant to turn the key.
  5. Test Relay Power Output: Requires multimeter/test light.
    • Identify the relay's high-current output terminal (to the fuel pump). Refer to diagram/manual.
    • Connect the multimeter (set to Volts DC) or test light between this output terminal and a known good ground (engine block, battery negative).
    • With the key turned ON, you should see battery voltage at this terminal for the 1-2 second prime cycle. No voltage confirms the relay is not switching high current, but use the swap test first.

Finding the Correct Replacement Relay

  1. Use the Original: Take the old relay with you to the parts store. It has manufacturer markings.
  2. Know the Specifications: The 1992 D150 fuel pump relay (typically the ASD relay) is a standard 4-pin or 5-pin relay meeting Bosch or ISO specifications. Most common number formats:
    • OEM Part Number: Original Chrysler number might be visible (e.g., 56027186, 56027357) - parts stores can cross-reference.
    • Industry Standard Numbers: Look for numbers like:
      • Standard Motor Products RY-110 or RY-291
      • BWD R3088
      • Echlin FF201 (older number - verify applicability)
      • Bosch 0-332-002-156
  3. Purchase Location: Available at AutoZone, O'Reilly, NAPA, Advance Auto Parts, RockAuto.com, or dealership parts departments.
  4. Quality Matters: Stick with known brands like Standard Motor Products, BWD, Bosch, or genuine Mopar. Cheap relays can fail prematurely.

Step-by-Step Replacement Guide

  1. Safety First: Ensure the truck is parked on level ground, transmission in Park (automatic) or gear (manual), parking brake firmly engaged. Disconnect the negative (-) battery cable. Secure it away from the battery terminal.
  2. Locate PDC and Relay: Identify the fuel pump/ASD relay in the PDC using the lid diagram.
  3. Remove Old Relay: Firmly grasp the relay and pull it straight up and out of its socket. It may require moderate force. Wiggle slightly if stuck but avoid twisting.
  4. Inspect Socket: Look into the relay socket where the old relay plugged in. Check for any signs of corrosion, bent pins, loose connections, or melted plastic. Clean any corrosion carefully with electrical contact cleaner and a small brush if needed. Do not proceed if the socket is damaged – repair may be needed.
  5. Install New Relay: Orient the new relay correctly (its terminals must align exactly with the socket pins). Gently push it firmly and straight down into the socket until it seats fully. You should hear or feel a distinct click.
  6. Reconnect Battery: Reattach the negative battery cable and tighten securely.
  7. Key ON Test: Turn the ignition key to the "ON" position. You should now clearly hear the fuel pump operate for 1-2 seconds to prime the fuel system. This is the critical confirmation.
  8. Start the Engine: Attempt to start the truck. It should start normally. Listen for smooth running.

Important Considerations & Troubleshooting

  • Fuses Always: If the relay was found blown or the fuel pump fuse was blown, replacing it is necessary. However, always investigate why it blew. A failing fuel pump drawing excessive current is a very common cause. If a new fuse blows immediately or soon after replacement, you likely have a short circuit or a bad fuel pump that needs addressing. Do not keep replacing fuses without addressing the underlying cause.
  • The "No Prime" Sound After Replacement: If you still hear no fuel pump prime sound after relay replacement:
    • Double-Check Installation: Confirm relay is firmly seated in the correct socket.
    • Check Main Fuses Again: Inspect large fuses related to fuel pump/PCM/Power Distribution in the PDC and the fusible links near the battery/starter relay.
    • Consider Fuel Pump Failure: If the relay is verified good (or was swapped and tested successfully) and gets power/switches correctly, the fuel pump itself or its wiring from the PDC to the tank might be faulty. Testing fuel pressure at the rail is the next diagnostic step.
    • Inertia Switch (If Equipped): Some models (especially trucks used for fleet/snowplow) might have a fuel pump inertia shutoff switch mounted in the cab (kick panel area) or under the dash. If tripped (e.g., from a bump), it cuts power to the pump. Find it and press the reset button.
    • PCM Control: Very rarely, the PCM itself could have failed to send the signal to ground the relay's control circuit. This requires advanced diagnostics.
  • Addressing Corrosion: If relay socket terminals are corroded, clean thoroughly with electrical contact cleaner spray and a plastic-bristled brush or contact cleaning tool. Protect with dielectric grease after cleaning and drying.
  • Spare Relay: Considering the age of the vehicle and the importance of this component, carrying a spare fuel pump/ASD relay in your glove box is highly recommended. It takes minimal space and can get you out of a sudden breakdown situation.

Long-Term Reliability Tips

  • Use Quality Parts: As mentioned, avoid the cheapest generic relays.
  • Socket Protection: Ensure the PDC lid seals properly to protect the relays and fuses from excessive moisture. Address any hood leaks that drip water into the engine bay near the PDC.
  • Regular Inspection: Periodically (e.g., during oil changes) open the PDC and visually check the main fuses and relays, including the fuel pump/ASD relay, for signs of overheating or corrosion.

Conclusion: Restoring Fuel Delivery
The 1992 Dodge D150 fuel pump relay, often integrated as the Auto Shutdown (ASD) relay, is a fundamental component for starting and running your truck. Failure presents with clear symptoms like no-start during cranking or sudden stalling. Diagnosis using the relay swap method is straightforward and highly effective. Locating the relay in the Power Distribution Center (PDC) under the hood is simple once you reference the lid diagram. Replacing a faulty relay is an uncomplicated repair that any owner can confidently perform with basic tools and attention to safety. Ensuring this critical switch operates correctly restores reliable fuel delivery, keeping your vintage D150 dependable for years to come. Always prioritize confirming the fix by listening for the distinct fuel pump prime sound upon key turn.

Back to blog