Main Relay

This procedure covers the replacement of the main relay (also known as the Automatic Shutdown Relay or ASD relay) in the Power Distribution Center, which controls power to the fuel injection system and ignition components.

Warnings

Tools required

Parts

• Main relay (ASD relay) × 1 — Use OEM specification

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn ignition to OFF position and remove key
3. Allow engine to cool if recently operated
4. Gather replacement relay and verify correct part number against vehicle specifications

Procedure

1. 1

   Disconnect battery negative terminal
   Open the hood and locate the battery. Using the battery terminal wrench, loosen and remove the negative (-) battery cable from both batteries (this Cummins diesel is equipped with dual batteries). Secure both cables away from the terminals. Secure the cable away from the battery to prevent accidental reconnection.
2. 2

   Locate Power Distribution Center
   The Power Distribution Center (PDC) is located in the engine compartment on the driver's side inner fender, near the battery. It is a black plastic box with a removable cover containing fuses and relays.
3. 3

   Remove PDC cover
   Release the locking tabs on the sides of the Power Distribution Center cover by pressing or pulling them outward. Lift the cover straight up to remove it. The relay and fuse diagram is printed on the underside of the cover for reference.
4. 4

   Identify the main relay
   Using the diagram on the PDC cover, locate the Automatic Shutdown Relay (ASD relay), which is the main relay. It is typically a larger relay in the center or front section of the PDC. Verify the relay location matches your specific vehicle's PDC diagram printed on the underside of the cover, as the exact cavity position for the ASD relay must be confirmed for this vehicle.
5. 5

   Remove the old relay
   Firmly grasp the main relay and pull it straight up out of its socket. The relay is held in place by friction in the socket terminals. Rock it gently side to side if needed, but do not twist or bend the relay. Inspect the socket terminals for any corrosion, melting, or damage.
6. 6

   Inspect relay socket
   Examine the relay socket for signs of overheating, corrosion, or damaged terminals. Look for melted plastic, discolored or burnt terminals, or debris in the socket. If damage is present, the entire PDC may need replacement or professional repair. Clean any minor corrosion with electrical contact cleaner if necessary.
7. 7

   Install new relay
   Align the new main relay with the socket, ensuring the relay pins match the socket configuration. Press the relay firmly into the socket until it is fully seated and flush with the surrounding relays. The relay should click into place and sit level in the PDC.
8. 8

   Reinstall PDC cover
   Position the Power Distribution Center cover over the PDC housing, aligning the cover with the edges. Press down firmly on all sides until the locking tabs engage and the cover is secure. Ensure the cover is properly sealed to prevent moisture intrusion.
9. 9

   Reconnect battery
   Reconnect the negative battery cable to the battery terminal and tighten securely with the battery terminal wrench. Ensure the connection is tight to prevent voltage drop or starting issues.

Reassembly

1. Ensure all PDC cover tabs are fully engaged and the cover is properly seated
2. Verify battery connection is tight and secure
3. Close hood after verification testing is complete

Verification

• Turn the ignition key to the ON position (do not start). The instrument cluster should illuminate normally and the check engine light should perform its bulb check
• Start the engine. It should crank and start normally without extended cranking
• Allow the engine to idle for 1-2 minutes and verify no warning lights remain illuminated
• Turn the engine off and restart to confirm proper relay operation
• Test accessories such as power windows and radio to confirm normal electrical system operation
• If the check engine light remains on, use a scan tool to check for diagnostic codes related to the ASD relay circuit

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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