Main Relay

Replace the main relay in a 2009 Aston Martin DB9, which controls primary electrical system power distribution. The relay is located in the engine compartment fusebox.

Warnings

Tools required

Parts

• Main relay (power distribution relay) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and ensure ignition is OFF with key removed.
2. Open hood and secure with prop rod.
3. Locate battery in engine compartment (driver side near firewall).
4. Using 10mm socket, loosen negative battery terminal bolt and disconnect negative cable. Secure cable away from terminal.
5. Wait minimum 2 minutes for electrical system capacitor discharge.
6. Locate main fusebox/relay panel on driver side of engine compartment near shock tower.

Procedure

1. 1

   Access fusebox cover
   Remove the fusebox cover by releasing the retaining clips. The cover typically has 2-4 clips around the perimeter. Gently pry or press release tabs to lift cover away from fusebox housing. Set cover aside in clean location with interior facing up to prevent contamination. Note: Open hood and verify it is supported by its gas struts (or prop rod if equipped) before working.
2. 2

   Identify main relay location
   Locate the main relay within the fusebox. It is typically labeled on the fusebox diagram (printed on underside of cover or on fusebox body). The main relay is usually a larger relay, often black or gray, positioned in a prominent location within the relay array. On the DB9, verify the main relay location against the fusebox diagram printed on the cover or body, as its exact position within the relay array should be confirmed rather than assumed. Verify relay identification by checking part number markings on relay body or consulting fusebox diagram. Note: On the DB9, consult the fusebox diagram (printed on the underside of the cover or in the owner's/workshop manual) to confirm the exact main relay position, as the layout varies. Note: On the DB9, consult the fusebox diagram to confirm the exact main relay location before removal, as position is not assumed.
3. 3

   Document relay orientation
   Before removal, note the orientation of the relay, specifically the position of any alignment tabs or keyed features. Take a photo if available, or mark the relay and socket position with a marker for reference during installation. This ensures correct reinstallation alignment.
4. 4

   Remove main relay
   Grasp the relay body firmly and pull straight upward to extract it from the socket. Apply even, steady pressure. Do not rock or twist excessively, as this may damage socket pins. If relay is difficult to remove, use a small flat-blade screwdriver to gently pry under relay edges while pulling upward, being careful not to damage adjacent relays or fusebox housing.
5. 5

   Inspect relay socket
   Examine the relay socket for corrosion, bent pins, or debris. Use compressed air or clean cloth to remove any dust or contamination from socket terminals. Check that all socket pins are straight and properly aligned. If corrosion is present, clean terminals with electrical contact cleaner and allow to dry completely before proceeding. Bent pins should be carefully straightened with needle-nose pliers.
   ⚠Do not apply excessive force when straightening socket pins, as they can break. If pins are severely damaged, the entire fusebox may require replacement.
6. 6

   Verify new relay specifications
   Compare the new relay to the old relay. Verify that part numbers match, and that physical dimensions, terminal configuration, and amperage ratings are identical. Check that alignment tabs and keying features match between old and new relays. Do not install a relay with different specifications, as this may cause electrical system damage or fire hazard.
7. 7

   Install new main relay
   Align the new relay with the socket, matching orientation noted during removal. Ensure alignment tabs or keyed features are properly positioned. Press relay firmly into socket with steady, even pressure until it seats completely. Relay should click or seat flush with adjacent relays. Verify relay is fully seated by attempting to gently lift it; there should be no vertical movement.
8. 8

   Reinstall fusebox cover
   Position fusebox cover over housing, aligning all retaining clips with their respective mounting points. Press cover down firmly until all clips engage with audible clicks. Verify cover is secure and flush with fusebox housing around entire perimeter.
9. 9

   Reconnect battery
   Reconnect the negative battery cable to the negative terminal in the luggage compartment (trunk). Ensure terminal contact surfaces are clean and free of corrosion. Tighten the terminal bolt to the Aston Martin factory-specified torque using a torque wrench; verify the exact value against factory documentation before tightening. Do not overtighten, as this can damage the battery terminal or cable.lt to the manufacturer-specified torque (approximately 6.0 Nm / 4.4 lb-ft) using a torque wrench. Note: Tighten terminal bolt to the manufacturer-specified torque (approximately 6.0 Nm / 4.4 lb-ft) using a torque wrench; verify the exact value against factory documentation.
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Verify fusebox cover is properly seated and all clips are engaged.
2. Ensure no tools or parts are left in engine compartment.
3. Close hood and verify proper latch engagement.

Verification

• Turn ignition to ON position (do not start engine). Verify dashboard warning lights illuminate normally, indicating relay is functioning and providing power to instrument cluster.
• Attempt to start engine. Engine should crank and start normally if relay was the sole issue.
• Verify all electrical accessories function properly: headlights, HVAC blower, power windows, radio, and other systems.
• If available, use diagnostic scan tool to verify no new electrical system fault codes are present.
• Road test vehicle to confirm no intermittent electrical issues occur under normal operating conditions.

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