Downpipe

Removal and replacement of the downpipe assembly connecting the catalytic converters to the exhaust system on the 2009 Aston Martin DB9 6.0L V12.

Warnings

Tools required

Parts

• Downpipe gasket set (catalytic converter to downpipe) × 1 — Use OEM specification
• Downpipe to mid-pipe gaskets × 1 — Use OEM specification
• Exhaust flange bolts and hardware kit × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and allow exhaust system to cool completely (minimum 2 hours after operation).
2. Raise vehicle on lift or secure on jack stands at manufacturer-specified lift points.
3. Spray all exhaust flange bolts, hanger bolts, and oxygen sensor threads with penetrating oil. Allow to soak for 15-30 minutes.
4. Ensure adequate ventilation if working indoors due to residual exhaust particulates.
5. Identify which bank (left or right) requires downpipe replacement and plan access accordingly.

Procedure

1. 1

   Disconnect oxygen sensors
   Locate the oxygen sensor(s) mounted on the downpipe assembly (verify which upstream/downstream sensors are present on the downpipe versus the cat/manifold per OEM documentation). Disconnect the electrical connectors by pressing the release tab and pulling away from the sensor body. Using an oxygen sensor socket, carefully remove both sensors from the downpipe. Turn counterclockwise with steady pressure. If sensors are seized, apply additional penetrating oil and allow to soak, or apply heat carefully with a propane torch to the bung (not the sensor itself). Store sensors in a clean location if reusing. Note: Locate the oxygen sensor(s) mounted on the downpipe assembly (verify which sensors — upstream and/or downstream — are present on this section against Aston Martin service documentation).
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
2. 2

   Remove heat shields
   Locate the heat shields covering the downpipe assembly. These are typically secured with Torx or E-Torx fasteners. Remove the fasteners securing the heat shields to the chassis and downpipe brackets. There are typically 4-6 fasteners per heat shield section. Carefully remove the heat shields and set aside. Inspect shields for damage or excessive corrosion.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
3. 3

   Disconnect downpipe from catalytic converter
   Locate the flange connection between the catalytic converter/manifold outlet and the downpipe inlet (verify the exact exhaust architecture — the DB9 V12 uses manifold-integrated catalytic converters — against OEM documentation). This connection uses a multi-bolt flange with a gasket. Remove the flange bolts (the exact count is unconfirmed — verify against Aston Martin OEM documentation before ordering hardware; do not rely on an assumed count). Use a combination of socket and universal joint if access is restricted. Support the downpipe weight with one hand or a jack stand as bolts are loosened to prevent binding. Once all bolts are removed, separate the flange connection. The gasket may be stuck; use a pry bar gently if needed. Note: Remove the flange bolts (verify exact count against OEM documentation for the DB9 V12). Note: Remove the flange bolts (verify exact count against Aston Martin service documentation for this flange).
   Torque spec

   Exhaust Flange Bolt25 Nm (18 lb-ft)
4. 4

   Disconnect downpipe from mid-pipe
   Move to the rear flange connection where the downpipe meets the mid-pipe section of the exhaust. This is also a flanged connection with bolts. Remove the flange bolts securing the downpipe to the mid-pipe assembly. Support the downpipe as bolts are removed. Once all fasteners are out, separate the flange connection. Note the orientation of the flange for reassembly.
   Torque spec

   Exhaust Flange Bolt25 Nm (18 lb-ft)
5. 5

   Remove exhaust hanger mounts
   Locate the rubber exhaust hangers supporting the downpipe assembly. The DB9 uses rubber hanger mounts attached to chassis brackets; verify the exact number and locations against OEM documentation. Use an exhaust hanger removal tool or carefully pry the rubber hangers off their mounting studs using a pry bar. Work methodically to avoid tearing the rubber. If hangers are severely deteriorated, note for replacement. Note: The DB9 uses rubber hanger mounts to support the downpipe section attached to chassis brackets (verify exact count against OEM documentation). Note: The downpipe section is supported by rubber hanger mounts attached to chassis brackets (verify exact count and locations against Aston Martin service documentation).
   Torque spec

   Hanger Bolts27 Nm (20 lb-ft)
6. 6

   Remove downpipe assembly
   With all connections and hangers released, carefully maneuver the downpipe assembly downward and out from the vehicle. The downpipe may need to be rotated or angled to clear suspension components, chassis members, and the transmission tunnel. Work slowly to avoid damaging brake lines, wiring harnesses, or other components. An assistant is helpful for this step due to the length and weight of the assembly.
7. 7

   Clean flange surfaces and inspect
   With the downpipe removed, thoroughly clean all flange mating surfaces on the catalytic converter outlet and mid-pipe inlet using a wire brush and gasket scraper. Remove all old gasket material, carbon buildup, and corrosion. Inspect flanges for warping, cracks, or damage. Check stud threads for damage and replace if necessary. Inspect catalytic converter outlet for deterioration or internal substrate damage. Check mid-pipe flange condition.
8. 8

   Prepare new downpipe for installation
   Inspect the new or replacement downpipe for shipping damage and verify correct fitment and side-specific (left/right bank) orientation; confirm the correct OEM part number for the bank being serviced against Aston Martin documentation, as left and right bank downpipes differ. Install new gaskets onto the flange surfaces. Apply a thin coat of anti-seize compound to all flange bolt threads and the first 2-3 threads of oxygen sensor bungs (avoid contaminating sensor tips or bung sealing surfaces). If reusing oxygen sensors, inspect them for damage and ensure tips are clean and undamaged.
9. 9

   Install downpipe assembly
   Maneuver the new downpipe into position, reversing the removal path. Align the inlet flange with the catalytic converter outlet flange and the outlet flange with the mid-pipe inlet flange. Engage the rubber exhaust hangers onto their mounting studs. An assistant is helpful to support the downpipe while aligning multiple connection points. Ensure all gaskets remain properly seated during alignment.
10. 10

    Connect and torque catalytic converter flange
    Install the flange bolts connecting the downpipe to the catalytic converter outlet. Start all bolts by hand to ensure proper thread engagement. Tighten bolts in a cross-pattern sequence to ensure even gasket compression. Torque all flange bolts to specification using a torque wrench.
    Torque spec

    Exhaust Flange Bolt25 Nm (18 lb-ft)
11. 11

    Connect and torque mid-pipe flange
    Install the flange bolts connecting the downpipe outlet to the mid-pipe inlet. Start all bolts by hand. Tighten in a cross-pattern to ensure even gasket seating. Torque all flange bolts to specification.
    Torque spec

    Exhaust Flange Bolt25 Nm (18 lb-ft)
12. 12

    Secure exhaust hangers
    Verify that all rubber exhaust hangers are fully seated on their mounting studs and that the downpipe hangs at the correct height without binding or excessive tension. Adjust hanger positions if necessary. If hanger bracket bolts were removed, reinstall and torque to specification.
    Torque spec

    Hanger Bolts27 Nm (20 lb-ft)
13. 13

    Install oxygen sensors
    Install the upstream and downstream oxygen sensors into their bungs on the downpipe. Apply anti-seize compound only to the sensor threads (first 2-3 threads), keeping compound away from the sensor tip and sealing washer area. Thread sensors in by hand initially to avoid cross-threading. Tighten sensors to specification using an oxygen sensor socket and torque wrench. Reconnect the electrical connectors to each sensor, ensuring they click securely into place.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
14. 14

    Reinstall heat shields
    Position the heat shields back over the downpipe assembly. Install all heat shield fasteners and tighten to specification. Ensure heat shields do not contact the downpipe or other components that could cause rattling or wear.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)
15. 15

    Final inspection and test
    Perform a visual inspection of all connections, ensuring no tools or parts were left in the work area. Check that all exhaust hangers are properly engaged and that the exhaust system hangs correctly without contacting the chassis or suspension. Lower the vehicle to the ground. Start the engine and listen for exhaust leaks at all flange connections. Rev the engine gently while listening and feeling for leaks. Check for proper oxygen sensor operation by monitoring for check engine lights or sensor fault codes using a diagnostic scanner.

Reassembly

1. Reassembly follows the reverse order of disassembly with attention to torque specifications.
2. Always use new gaskets at all flange connections.
3. Apply anti-seize compound to all exhaust fastener threads and oxygen sensor threads as specified.
4. Torque all fasteners in cross-pattern sequences where applicable to ensure even gasket compression.
5. If replacing both bank downpipes, repeat the entire procedure for the opposite side.

Verification

• Start engine and listen carefully at all flange connections for exhaust leaks (hissing or ticking sounds).
• Check oxygen sensor electrical connections are secure and sensors are functioning (no check engine light).
• Perform a test drive and monitor for abnormal exhaust sounds, vibrations, or drone.
• After 50-100 miles of driving, re-torque all flange bolts to specification as exhaust gaskets may settle.
• Use a diagnostic scanner to verify all oxygen sensors are reading correctly and no exhaust-related fault codes are present.

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