Alternator

This procedure replaces the alternator on a 2009 Aston Martin DB9 with 6.0L V12 engine, requiring partial disassembly of front underbody panels and serpentine belt removal to access the alternator mounted low on the engine.

Warnings

Tools required

Parts

• Alternator × 1 — Use OEM specification
• Serpentine belt (if worn or contaminated) × 1 — Use OEM specification

Preparation

1. Park vehicle on level ground and engage parking brake
2. Allow engine to cool completely (minimum 2 hours after operation)
3. Gather all tools and new alternator before beginning
4. Photograph serpentine belt routing for reference before removal
5. Place wheel chocks behind rear wheels

Procedure

1. 1

   Disconnect battery negative terminal
   Locate the battery, which on the 2009 DB9 is located in the luggage compartment (boot) rather than the engine bay. Using a 10mm socket, loosen the negative (-) battery terminal bolt and remove the cable from the terminal. Secure the cable away from the battery post to prevent accidental reconnection during the repair. Note: Locate the battery (on the 2009 DB9 the battery is in the luggage/trunk compartment, not the engine bay — verify exact location and access panel in the owner's/service manual).
   Torque spec

   Battery Terminal Bolts8 Nm (6 lb-ft)
2. 2

   Raise and support vehicle
   Lift the front of the vehicle using a floor jack at the factory-designated front jacking points (verify exact jacking point locations in Aston Martin documentation to avoid damaging the aluminum bonded chassis). Once raised to working height, place jack stands under the front subframe or chassis rails. Lower the vehicle onto the jack stands and verify stability before working underneath. Ensure adequate clearance to access the front undertray. Note: Lift the front of the vehicle using a floor jack at the factory-designated front jacking points only. Once raised to working height, place jack stands under the factory-specified aluminum chassis lift points (verify exact locations in the Aston Martin service manual, as improper placement can damage the bonded aluminum structure).
   ⚠Verify jack stands are positioned on solid structural points, not on plastic panels or suspension components.
3. 3

   Remove front undertray panels
   From underneath the vehicle, identify the front undertray panels protecting the engine compartment. Remove the Torx fasteners securing the panels (typically T30 or T40). There are approximately 12-16 fasteners total across the front and center sections. Some fasteners may be clips or quick-release types. Work from front to rear, supporting the panels as you remove the last fasteners to prevent them from falling. Set panels aside in a safe location.
4. 4

   Locate alternator and document belt routing
   With the undertray removed, locate the alternator on the engine. Verify its exact position against factory documentation for the 2009 DB9 6.0L V12, as the alternator mounting location and access direction (from above or below) must be confirmed before proceeding. The alternator will have the serpentine belt wrapped around its pulley. If not already done, take a clear photograph of the serpentine belt routing path across all pulleys, or sketch the routing pattern. Note the position of the belt tensioner (verify exact tensioner location against Aston Martin service documentation for the 2009 DB9 6.0L V12). Note: With the undertray removed, locate the alternator on the front accessory drive of the engine (verify exact position against factory service documentation for the 2009 DB9 V12).
   ℹ️Accurate belt routing documentation is critical. An incorrectly routed belt can cause noise, premature wear, or accessory failure.
5. 5

   Release serpentine belt tension and remove belt
   Locate the serpentine belt tensioner pulley. Using a 3/8" breaker bar or serpentine belt tool, insert into the tensioner's square drive socket and rotate the tensioner in the direction specified by the factory service documentation to release tension on the belt (direction is not assumed here — confirm for the 2009 DB9 V12 before applying force). While holding tension released, slide the belt off the alternator pulley first, then release the tensioner slowly. Remove the belt completely from all pulleys and set aside. Inspect the belt for cracks, glazing, or oil contamination; replace if any damage is present.
6. 6

   Disconnect alternator electrical connections
   At the rear of the alternator, locate the main electrical connector and the battery positive cable connection. Press the release tab on the main connector and pull it straight off the alternator. For the battery positive terminal, remove the protective rubber boot if present, then use the appropriate socket (verify exact size against Aston Martin documentation for the 2009 DB9) to remove the nut securing the cable lug to the alternator B+ stud. Remove the cable and set it aside, being careful not to let it contact ground.
   ⚠Although the battery is disconnected, the positive cable may still carry residual charge or could short if it contacts the chassis. Handle carefully.
7. 7

   Remove alternator mounting bolts
   The alternator is secured by 2 or 3 mounting bolts to the engine block or mounting bracket. Identify all mounting bolts (typically one upper pivot bolt and one or two lower mounting bolts). Using the appropriate socket (verify exact size against Aston Martin documentation for the 2009 DB9 6.0L V12; mounting bolt heads may be hex or Torx), remove each mounting bolt completely. Support the alternator with one hand as you remove the final bolt to prevent it from falling. The alternator may be tight in its mounting location; gently rock it to break it free if necessary.
   Torque spec

   Alternator Mounting Bolts25 Nm (18 lb-ft)

   Alternator Pivot Bolt25 Nm (18 lb-ft)
8. 8

   Remove alternator from vehicle
   Carefully maneuver the alternator out of its mounting location. Due to tight clearances in the V12 engine bay, you may need to angle the alternator and manipulate it past hoses, brackets, or other components. Work slowly to avoid damaging surrounding parts. Once clear, lower the alternator down and out from underneath the vehicle.
   ℹ️The alternator is heavy (typically 10-15 lbs) and the access is awkward. Use both hands and avoid dropping it onto yourself or other components.
9. 9

   Prepare new alternator for installation
   Unpack the new alternator and verify it matches the original unit in mounting configuration, pulley type, and electrical connections. Clean the alternator mounting surfaces on the engine block with a wire brush to remove any rust, debris, or old gasket material. Apply a small amount of dielectric grease to the electrical terminals on the new alternator to prevent corrosion. Verify all mounting bolt threads in the engine block are clean and undamaged.
   ℹ️Do not apply grease or anti-seize to the mounting bolt threads unless the factory specification calls for it. Doing so can affect torque readings.
10. 10

    Install new alternator
    Position the new alternator into the mounting location, angling and maneuvering it past obstructions as necessary. Align the mounting holes with the corresponding threaded holes in the engine block or bracket. Start all mounting bolts by hand to ensure proper thread engagement before tightening any of them. Once all bolts are hand-started, use a torque wrench to tighten each bolt evenly to the factory-specified torque for the 2009 DB9 6.0L V12. VERIFY exact torque values for the mounting and pivot bolts against Aston Martin service documentation before final tightening, as these may differ. Note: Once all bolts are hand-started, use a torque wrench to tighten each bolt in a star or alternating pattern to the factory-specified torque (verify exact value and bolt size in the Aston Martin service manual before final tightening).
    ⚠Overtightening alternator bolts can strip threads in the aluminum engine block or crack the alternator housing. Use a calibrated torque wrench.
    Torque spec

    Alternator Mounting Bolts25 Nm (18 lb-ft)

    Alternator Pivot Bolt25 Nm (18 lb-ft)
11. 11

    Reconnect alternator electrical connections
    Reattach the battery positive cable lug to the B+ stud on the alternator. Install the nut and tighten securely using the appropriate socket, but do not over-torque (typically hand-tight plus 1/4 turn). Replace the protective rubber boot over the terminal. Reconnect the main electrical connector to the alternator, pressing firmly until you hear or feel the locking tab click into place. Verify the connection is secure by gently tugging on it.
    ℹ️Ensure connectors are fully seated. Partial connections can cause charging system faults or no-start conditions.
12. 12

    Install serpentine belt
    Referring to your routing diagram or photograph, route the new or existing serpentine belt around all pulleys except the alternator pulley. Ensure the belt is seated properly in each pulley groove as you route it. Using the breaker bar, rotate the belt tensioner to create slack, then slip the belt over the alternator pulley last. Slowly release the tensioner, ensuring the belt is properly seated on all pulleys and the tensioner has full contact with the belt. Visually verify correct belt alignment on all pulleys.
    ⚠Keep hands and tools clear of pulleys and belt as tensioner is released. Belt can snap into place with significant force.
13. 13

    Reinstall front undertray panels
    Position the undertray panels back under the vehicle, aligning them with their original mounting locations. Install all Torx fasteners, clips, and quick-release fasteners, working from rear to front. Ensure panels are seated flush and no gaps are present. Tighten fasteners snugly but do not over-tighten plastic clips.
    ℹ️Over-tightening plastic undertray fasteners can crack the panels or strip clips. Tighten until snug, then stop.
14. 14

    Lower vehicle and reconnect battery
    Raise the vehicle slightly with the floor jack to unload the jack stands, then remove the jack stands and carefully lower the vehicle to the ground. Using a 10mm socket, reconnect the negative battery terminal to the battery post and tighten the terminal bolt to the factory-specified torque (verify against Aston Martin documentation for the 2009 DB9). Do not over-tighten. Note: Reconnect the negative battery terminal to the battery post and tighten the terminal clamp bolt to the factory-specified torque (verify value in the Aston Martin service manual).
    ⚠Ensure the negative terminal is the last connection made to prevent accidental shorts during installation.
    Torque spec

    Battery Terminal Bolts8 Nm (6 lb-ft)
15. 15

    Start engine and verify charging system operation
    Start the engine and allow it to idle. Observe the instrument cluster for any warning lights related to the charging system (battery light should extinguish within 2-3 seconds). Using a multimeter, measure voltage at the battery terminals with the engine running at idle; it should read approximately 13.8-14.5 volts, indicating proper alternator charging. Rev the engine to 2000 RPM and verify voltage remains stable. Listen for any unusual noises from the alternator or belt area.
    ℹ️If the battery warning light remains illuminated or voltage is not within specification, shut off the engine immediately and recheck all electrical connections and belt installation.

Reassembly

1. Reassembly is covered in the procedure steps above, as each removal step is immediately followed by its corresponding installation step
2. Ensure all electrical connections are secure and protected from moisture
3. Verify serpentine belt is correctly routed and seated on all pulleys before final operation
4. Double-check that all undertray panels are reinstalled to protect components from road debris

Verification

• Battery warning light extinguishes within 2-3 seconds of engine start
• Charging system voltage measures 13.8-14.5 volts at idle with engine running
• No unusual noises from alternator or belt during engine operation
• Serpentine belt tracks centered on all pulleys without misalignment or slipping
• All undertray panels are secure with no loose fasteners
• No warning lights or fault codes related to charging system present

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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