Fuel Pump Relay

This procedure replaces the fuel pump relay in the Power Distribution Center (PDC) under the hood, which controls power to the fuel lift pump on the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• Fuel pump relay × 1 — Standard automotive mini relay, 40A rating recommended

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn ignition to OFF position and remove key
3. Open hood and secure with prop rod
4. Disconnect negative battery cable and wait 2 minutes for system capacitors to discharge
5. Locate the Power Distribution Center (black rectangular box) on the driver side of engine compartment near firewall

Procedure

1. 1

   Remove PDC cover
   Release the locking tabs on the sides of the Power Distribution Center cover. There are typically two tabs on each long side. Carefully pry up the tabs with a flathead screwdriver or trim tool and lift the cover straight up to remove. The relay diagram is printed on the underside of this cover.
2. 2

   Identify fuel pump relay location
   Locate the fuel pump relay using the diagram on the underside of the PDC cover you just removed. On 2007 Ram 3500 with 5.9L Cummins, identify the fuel pump relay strictly by cross-referencing the position labeled on the PDC cover diagram (do not assume a symbol or label wording). Confirm whether it is a 4-pin or 5-pin relay by inspecting the removed unit. Note the relay position for correct replacement.
3. 3

   Remove old fuel pump relay
   Firmly grasp the old relay and pull straight up with steady pressure. The relay is held by friction fit into the socket. If difficult to remove, gently rock it side-to-side while pulling upward. Do not use excessive force or pry tools that could damage the relay socket pins.
4. 4

   Inspect relay socket
   Examine the relay socket for corrosion, bent pins, or heat damage. All pins should be straight and free of green or white corrosion. If corrosion is present, clean pins with electrical contact cleaner and allow to dry. Check for any signs of melting or burning which would indicate an electrical problem requiring further diagnosis.
5. 5

   Verify new relay specifications
   Before installation, confirm the new relay matches the specifications of the original. Verify pin configuration matches the original (4-pin or 5-pin), amperage rating matches or exceeds the original relay's rating, and voltage rating is 12V. The relay should have the same physical dimensions and mounting tab orientation as the original.
6. 6

   Install new fuel pump relay
   Align the new relay with the socket, ensuring the mounting tab matches the socket orientation. The relay will only fit one way due to the keyed design. Press the relay firmly straight down into the socket until it is fully seated and sits flush with surrounding relays. Ensure it is not tilted or partially inserted.
7. 7

   Reinstall PDC cover
   Position the PDC cover over the relay box, aligning all edges. Press down firmly on all sides until you hear the locking tabs click into place. Verify the cover is secure and sits flush with no gaps.
8. 8

   Reconnect battery
   Reconnect the negative battery cable(s) to the battery terminal(s). Note that the 2007 Ram 3500 Cummins uses dual batteries; reconnect the negative cable that was disconnected. Tighten the cable clamp securely to ensure good electrical contact.

Reassembly

1. Ensure PDC cover is fully latched on all sides
2. Verify no tools or parts are left in engine compartment
3. Close hood securely

Verification

• Turn ignition key to ON position (do not start engine). Listen for the fuel lift pump to run for approximately 30 seconds to prime the fuel system. You should hear a humming sound from the driver side frame rail area where the lift pump is mounted.
• Start the engine and verify it starts normally without extended cranking. The engine should fire within 5-10 seconds of cranking.
• Allow engine to idle for 2-3 minutes and verify smooth operation with no stumbling or fuel starvation symptoms.
• Turn engine off, wait 10 seconds, then restart to confirm proper relay function on subsequent starts.
• If engine fails to start or fuel pump does not activate, recheck relay installation, verify correct relay type, and inspect relay socket pins for proper contact.

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