Main Relay

Replace the main relay (also known as the Power Distribution Center relay or ignition run/start relay) located in the engine compartment, which controls power delivery to key vehicle systems.

Warnings

Tools required

Parts

• Main relay (ignition run/start relay) × 1 — Verify relay location in Power Distribution Center - typically labeled as Ignition Off Draw (IOD) fuse/relay or Auto Shutdown Relay

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition to OFF position and remove key
3. Open hood and secure with hood prop
4. Disconnect negative battery cable and isolate away from battery post

Procedure

1. 1

   Locate Power Distribution Center
   The Power Distribution Center (PDC) is located in the engine compartment; verify its exact position against the 2008 Viper service manual before proceeding. It is a black plastic box with an integrated cover containing fuses and relays. It is a black plastic box with an integrated cover containing fuses and relays. Identify the PDC - it will have a diagram on the underside of the cover showing relay and fuse positions.
2. 2

   Remove PDC cover
   Release the cover tabs on the Power Distribution Center. The cover typically has 2-4 snap tabs along the edges. Gently pry or pull the tabs to release them, then lift the cover away to expose the relays and fuses inside. Set the cover aside with the diagram facing up for reference.
3. 3

   Identify main relay position
   Using the diagram on the PDC cover, locate the main relay. On the 2008 Viper, identify the correct relay from the PDC diagram and service manual — do NOT assume the IOD, ASD, and 'main' relay are the same component, as the IOD is typically a fuse controlling parasitic draw while the ASD relay powers the fuel/ignition system. Confirm the exact relay designation for the circuit you are servicing before removal. The relay will be a rectangular or square component with multiple blade terminals on the bottom, typically larger than standard mini-blade fuses. Note the relay orientation and terminal configuration before removal.
4. 4

   Remove failed main relay
   Grasp the relay firmly by the body and pull straight upward with steady, even pressure to remove it from the socket. If the relay is difficult to remove by hand, use needle-nose pliers to grip the relay body (not the terminals) or use a relay puller tool if available. Avoid rocking the relay side-to-side excessively, which can damage the socket terminals.
5. 5

   Inspect relay socket
   Examine the relay socket in the PDC for any signs of corrosion, melting, or damage to the terminal contacts. Check for burnt or discolored plastic around the socket. If corrosion is present on the terminals, clean with electrical contact cleaner and allow to dry. If the socket shows heat damage or melted plastic, the entire PDC may require replacement.
6. 6

   Install new main relay
   Align the new relay with the socket, ensuring the terminal configuration matches the socket layout and the relay is oriented correctly according to the PDC diagram. Press the relay straight down into the socket with firm, even pressure until it is fully seated and the terminals are flush with the bottom of the relay body. The relay should sit level and secure in the socket without rocking.
7. 7

   Reinstall PDC cover
   Position the Power Distribution Center cover over the relay/fuse box, aligning the cover tabs with the corresponding slots on the PDC body. Press down firmly on the cover edges until all tabs snap into place and the cover sits flush. Verify the cover is secure and will not come loose during vehicle operation.
8. 8

   Reconnect battery
   Reconnect the negative battery cable to the negative battery post and tighten the cable clamp securely. Ensure good metal-to-metal contact and that the cable cannot be pulled free by hand.

Reassembly

1. All components are reinstalled during the main procedure steps

Verification

• Turn ignition to ON position (engine off) and verify dash lights illuminate normally, indicating relay is providing power to ignition circuits
• Start the engine and verify it cranks and runs normally without any warning lights related to electrical system or fuel pump operation
• Test operation of accessories (radio, power windows, HVAC) to confirm proper power distribution through the relay
• Turn off engine and verify accessories shut down properly when ignition is turned to OFF position
• Check that there are no blown fuses in the PDC after relay replacement

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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