1999 Dodge Cummins Fuel Pump Relay Location: Your Essential Diagnostic & Repair Guide

Finding the fuel pump relay on your 1999 Dodge Ram with the Cummins 5.9L diesel engine is straightforward: it's located in the under-hood Power Distribution Center (PDC), specifically in position #9. The PDC is a large black plastic box usually found near the battery on the driver's side of the engine compartment.

This simple answer is crucial because a faulty fuel pump relay is a common culprit behind a no-start condition or an unexpected engine stall in your 24-valve Cummins. Knowing exactly where to look saves valuable time and frustration during diagnosis and repair. This guide provides comprehensive, practical information to locate, test, and replace this critical component on your 1999 Dodge Cummins, empowering you to get your truck back on the road.

Understanding the Power Distribution Center (PDC)

  • What it is: The PDC is the primary hub for electrical power distribution and circuit protection in your Dodge Ram. It houses numerous fuses and relays that control essential vehicle functions like the starter, headlights, horn, and of course, the fuel pump.
  • Location: Open the hood. Look for a large, rectangular, black plastic box with a lid, almost always situated near the battery on the driver's side (left side) fenderwell. It may be mounted directly on the fenderwell or on a bracket adjacent to the battery.
  • Access: To access the fuses and relays inside, simply unlatch the PDC lid (usually by pressing tabs on the sides) and lift it off. The inside of the lid typically contains a comprehensive diagram labeling every fuse and relay position and its associated function. Always consult this diagram first. It's your definitive map.
  • Why the PDC Matters: Placing relays like the fuel pump relay in a centralized location simplifies wiring, protects components from excessive engine heat, and makes diagnostics and servicing much easier. Corrosion or moisture intrusion can sometimes occur inside the PDC, leading to connection issues.

Locating the Fuel Pump Relay (Position #9)

  1. Safety First: Ensure the engine is OFF, the parking brake is engaged, and the ignition key is removed.
  2. Open the Hood: Locate the Power Distribution Center (PDC) near the battery on the driver's side fenderwell.
  3. Remove PDC Lid: Press the release tabs on the sides (or sometimes the ends) of the PDC cover and lift it straight off. Place it aside safely.
  4. Identify the Diagram: Carefully inspect the inside of the PDC lid you just removed. This diagram is critical and specifically keyed to your truck model, engine, and build date.
  5. Find Position #9: Examine the diagram closely. You are looking for the square representing Relay Position #9. Directly next to or below it on the diagram, you will see its labeled function. On all 1999 Dodge Rams with the 5.9L Cummins diesel engine, this position should be clearly labeled as the "AUTOMATIC SHUTDOWN (ASD) RELAY".
  6. Physically Locate #9: Inside the PDC itself, look for the row or column of identical-looking black plastic cubes (the relays). Each slot in the plastic base will have a number molded into it. Find the slot clearly marked "9".
  7. Identify the Relay: The relay plugged into slot #9 is the ASD Relay. While it might be tempting to call it simply the "fuel pump relay," its official and correct designation is the Automatic Shutdown (ASD) Relay. It's a standard automotive mini-ISO relay, approximately 1 inch square.

Crucial Clarification: The ASD Relay vs. the "Fuel Pump Relay"

  • Understanding the ASD Relay: On the 1999 Cummins 24V, the component found in position #9 of the PDC is specifically called the Automatic Shutdown (ASD) Relay. This terminology is critical for purchasing the correct replacement part.
  • Its Vital Role: The ASD Relay performs a dual function. It provides switched 12V power to both the fuel shutoff solenoid on the injection pump and the engine's ignition system components. When the ASD relay is energized (meaning the ignition key is turned to "Run" and the computer recognizes conditions are safe), it supplies power that allows fuel to flow through the injection pump and the injectors to fire.
  • Why it's Often Called the Fuel Pump Relay: Since the engine shuts down primarily by cutting fuel via the shutoff solenoid, and the ASD relay is the component enabling fuel delivery, many owners and mechanics casually refer to it as the "fuel pump relay." However, this engine does not have an in-tank, electrically powered "fuel pump" like a gasoline engine. Diesel engines rely on the high-pressure injection pump to draw fuel from the tank. The critical electrical component on the Cummins is the fuel shutoff solenoid controlled by the ASD relay.
  • Key Takeaway: For practical purposes of diagnosis and repair related to a no-fuel/no-start condition, locating and testing the relay in PDC position #9 is the correct procedure on a 1999 Dodge Cummins. Just be aware that its official name is ASD Relay.

Symptoms of a Faulty ASD/Fuel Pump Relay

Recognizing the signs can point you towards checking this relay:

  • Engine Cranks but Won't Start: This is the most common symptom. The starter turns the engine over normally, but there is no sign of ignition or fuel delivery.
  • Engine Stalls Unexpectedly: While driving, the engine suddenly dies as if the ignition key was turned off. It may restart immediately after or require a waiting period (cool down).
  • Intermittent Starting Problems: The truck sometimes starts fine, other times it just cranks without starting. These problems might correlate with engine temperature or humidity.
  • No Power to Fuel Shutoff Solenoid: You can verify this electrically (see testing section below).
  • Relay Clicking Audibly: Sometimes, a failing relay will make a rapid clicking sound when you turn the key to "Run," indicating it's trying unsuccessfully to engage its internal contacts. A silent relay when it should click is also a sign.

How to Test the 1999 Dodge Cummins Fuel Pump (ASD) Relay

Testing the relay itself is relatively simple before replacing it:

  • Audible Test (Preliminary): With the PDC lid removed and the ignition OFF, carefully plug the relay securely back into slot #9. Turn the ignition key to the "Run" position (DO NOT CRANK). You should hear a distinct single "CLICK" from the relay as it energizes. Turn the key back to "OFF." You may hear a faint de-energizing click. A clicking sound doesn't guarantee the internal contacts are good, but a lack of a click suggests a control circuit issue or a very dead relay.
  • Physical Swap Test: The most reliable functional test without tools is substitution. Find another relay in the PDC that is identical and controls a non-essential circuit (like the horn relay – check the diagram on the lid!). Carefully swap the suspected ASD relay (from slot #9) with the known good horn relay. If your horn suddenly stops working and the engine now starts, you've confirmed the original ASD relay is faulty.
  • Voltage Test (Advanced): Requires a multimeter.
    1. Identify relay socket pins: With the relay removed from slot #9, look at its base with the blade terminals pointing down. The standard mini-ISO relay pinout is:
      • Terminal 30: Constant B+ (Battery positive, usually fused)
      • Terminal 85: Relay Coil Ground (Controlled by ECM/PCM)
      • Terminal 86: Relay Coil Power (From ignition switch in "Run")
      • Terminal 87: Switched Output (To ASD Circuit - fuel solenoid/ignition)
      • Terminal 87a: Typically unused in this application.
    2. Test for Power: Set multimeter to DC Volts (20V scale).
      • Constant Power: Find the terminal in socket #9 that corresponds to Pin 30 (usually a thick wire). Ground the meter's black lead to the battery negative. Touch the red lead to the Pin 30 socket. You should read approximately battery voltage (12V+).
      • Ignition Power: Find the terminal in socket #9 that corresponds to Pin 86. Turn ignition to "Run." Ground black lead, red lead on Pin 86 socket. Should read approximately battery voltage. Turn key off.
      • Control Ground: Find Pin 85 socket. Turn ignition to "Run." Touch red multimeter lead to Pin 85 socket and black lead to battery positive. Or, touch black lead to a good ground (chassis/battery negative) and red lead to Pin 85 socket. You should read approximately battery voltage. (Contradictory readings indicate an issue with the ECM/PCM ground command).
    3. Test Relay Coil (Bench Test): Remove the relay. Set multimeter to Ohms or Continuity (beep). Measure resistance between Terminals 85 and 86. Most good relays read between 50 and 120 ohms. An open circuit (OL or very high ohms) indicates a bad coil. Low resistance (close to 0 ohms) might indicate a shorted coil.
    4. Test Relay Contacts (Bench Test): Place relay on a bench. With NO power applied, test continuity (Ohms/Beep) between Terminal 30 and Terminal 87. It should be Open Circuit (OL / no beep). Apply 12V to Terminal 86 and Ground to Terminal 85 (using jumper wires if necessary, e.g., from the battery). With power applied, you should now hear a click and get continuity (near 0 ohms / beep) between Terminal 30 and 87. If no continuity appears when powered, the relay contacts are faulty.

Replacing the Faulty ASD/Fuel Pump Relay

Once diagnosed as faulty, replacement is simple:

  1. Source the Correct Relay: Purchase a replacement Automotive Mini-ISO Relay, matching the configuration (typically 30/40 Amp) of the original. Genuine Mopar (part number may vary by build date, e.g., 04891708AD), Bosch, or quality aftermarket brands (BWD, Standard Motor Products) are reliable choices. Confirm it matches your original physically.
  2. Disconnect Battery: To prevent electrical shorts, disconnect the negative (-) battery terminal. Always best practice.
  3. Locate PDC Slot #9: Open hood, remove PDC lid, identify slot #9.
  4. Remove Old Relay: Grasp the faulty relay firmly and pull it straight out of its socket. It may require a slight wiggle but shouldn't need excessive force. Rocking it gently side-to-side while pulling straight can help. Avoid pulling only on the plastic top if possible.
  5. Install New Relay: Align the blade terminals on the bottom of the new relay with the corresponding slots in socket #9. Push it down firmly and evenly until it clicks or is fully seated. Ensure it sits flat like the surrounding relays.
  6. Reconnect Battery: Reattach the negative battery cable.
  7. Test Operation: Turn the ignition key to the "Run" position and listen for the distinct relay "click." If equipped, you might also hear the fuel shutoff solenoid energize briefly (a "clunk" near the injection pump). Attempt to start the engine.
  8. Reassemble: Replace the PDC lid securely, ensuring the latches engage properly. Close the hood.

Troubleshooting Tips if the New Relay Doesn't Fix the Problem

  1. Check Fuses: While you have the PDC lid off, carefully inspect the fuses associated with the ASD circuit. Relevant ones might include the large fuses (Maxi-fuses) supplying the PDC itself (check diagram), or smaller fuses. Replace any blown fuses, but investigate what caused the blow.
  2. Inspect PDC & Socket: Examine socket #9 closely. Look for signs of overheating (melted plastic, discolored terminals), corrosion (green/white powdery deposits on the metal terminals), or bent/damaged pins inside the socket. Clean corrosion gently with electrical contact cleaner and a brass brush if accessible. Repairing a damaged socket is more complex and may require professional wiring skills.
  3. Verify Fuel Shutoff Solenoid: If the relay is clicking and has good output voltage (see testing), the issue might lie downstream at the fuel shutoff solenoid itself or its wiring. You can briefly attempt to power the solenoid directly with 12V (exercise extreme caution; disconnect wiring first) to see if it clicks open. Resistance checks across the solenoid terminals can reveal an open coil.
  4. Diagnose ASD Control Circuit: If the relay receives constant power and ignition-switched power, but does not receive its ground signal from the ECM/PCM when the ignition is in "Run," the problem is in the control circuit. This could involve the ECM/PCM itself, faulty crank/cam sensors (which the ECM needs to see to engage the ASD), damaged wiring, or ground issues. Diagnostic trouble codes (DTCs) scanned via OBD-II should be checked for clues. This level of diagnosis often requires specialized tools or a professional technician.
  5. Consider Fuel System Issues: Don't forget that problems like a clogged fuel filter (very common!), water separator issues, blocked fuel pickup tube in the tank, or air intrusion in the fuel lines can mimic ASD relay failure symptoms by preventing fuel flow, even if the relay and solenoid are working correctly. Listen at the fuel tank filler neck for the distinct "clunk" of the solenoid opening when the key is turned to "Run" – hearing this confirms the relay and solenoid are functioning electrically at that moment.

Importance of Quality Parts

Using a high-quality replacement ASD relay is critical for the long-term reliability of your Cummins. Cheap, poorly constructed relays can fail prematurely, overheat, and potentially damage the PDC socket due to high resistance or welded contacts. Genuine Mopar parts offer OEM assurance, while reputable aftermarket brands provide a good balance of cost and reliable performance.

Beyond the 1999 Model Year

While this guide focuses specifically on the 1999 Dodge Ram 2500/3500 with the Cummins 5.9L diesel, it generally applies to the entire second-generation Dodge Rams (1994 through 2002 models). The ASD relay is consistently found in position #9 of the under-hood PDC throughout this generation. It's always best practice to verify the relay position using the diagram inside your specific truck's PDC lid.

Third Generation Dodge Ram (2003 and Newer): For owners of newer trucks (2003-2009 Classic or 2010+), note that Dodge/Ram significantly changed the electrical architecture. These trucks utilize a "TIPM" (Totally Integrated Power Module) which integrates the fuses, relays, and body control computer functions into one large unit, usually located under the hood near the battery. The fuel pump relay (or pump driver module, depending on year and pump type) is contained within the TIPM. Diagnosis and replacement become much more complex and often involve specialized procedures or module replacement. Consulting service information specific to your model year and engine is essential for these newer trucks.

Maintenance Considerations

While relays aren't typical "maintenance" items, some proactive steps can reduce problems:

  • Ensure the PDC lid is always properly sealed and latched to prevent moisture ingress leading to corrosion.
  • Periodically (during oil changes perhaps) inspect the PDC for debris or signs of water entry. Check the ASD relay visually for cracks or damage.
  • When cleaning the engine bay, avoid spraying water directly at the PDC.

Conclusion

Knowing the 1999 Dodge Cummins fuel pump relay location is definitively in the under-hood Power Distribution Center (PDC), Position #9 provides the critical starting point for diagnosing many common no-start conditions. Understanding that this relay is officially the Automatic Shutdown (ASD) Relay managing both fuel and ignition power unlocks accurate troubleshooting and parts ordering. By following the detailed steps outlined above for location, identification, testing (audible, swap, and multimeter methods), and replacement, you possess the practical knowledge to address one of the most frequent electrical failures on these robust trucks. Always prioritize safety by disconnecting the battery, double-check the PDC lid diagram specific to your truck, use quality replacement parts, and consider deeper system diagnostics if the relay replacement alone doesn't solve your starting issue. Mastering this essential piece of Cummins knowledge empowers you to keep your 1999 Dodge Ram 2500/3500 running reliably.

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