Downpipe

This procedure covers the removal and installation of the downpipes on the 2007-2013 Mercedes-Benz S65 AMG with the M275 6.0L V12 BiTurbo engine, including oxygen sensor handling and exhaust flange connections.

Warnings

Tools required

Parts

• Downpipe (left) × 1 — Use OEM specification or performance aftermarket
• Downpipe (right) × 1 — Use OEM specification or performance aftermarket
• Exhaust flange gaskets (turbo to downpipe) × 2 — Mercedes-Benz OEM or equivalent high-temp gasket
• Exhaust flange gaskets (downpipe to mid-pipe) × 2 — Mercedes-Benz OEM or equivalent
• Oxygen sensors (pre-catalytic converter) × 2 — A0009053603 or equivalent (if reusing, inspect condition)
• Exhaust flange bolts/nuts × 1 — Replace if corroded or damaged
• Anti-seize compound × 1 — High-temperature nickel-based

Preparation

1. Park vehicle on level surface and allow exhaust system to cool completely (minimum 2 hours after operation).
2. Disconnect negative battery terminal to prevent oxygen sensor fault codes during removal.
3. Raise vehicle on lift or secure on jack stands with adequate clearance for undercarriage access.
4. Remove engine undercover panels and heat shields to access downpipes.
5. Apply penetrating oil to all exhaust flange bolts, oxygen sensors, and hanger bolts; allow to soak while preparing tools.
6. Locate and disconnect oxygen sensor electrical connectors for both pre-catalytic converter sensors (one per bank).

Procedure

1. 1

   Remove heat shields
   Remove the heat shields surrounding the turbochargers and downpipe area. These are secured with multiple bolts around the V12 engine bay. Remove all heat shield bolts and carefully extract shields, noting their orientation for reinstallation.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
2. 2

   Disconnect oxygen sensors
   Using the oxygen sensor socket, carefully remove both pre-catalytic converter oxygen sensors from the downpipes. Turn counterclockwise while supporting the sensor body. If sensors are seized, apply additional penetrating oil and allow to soak, then use gentle heat if necessary. Inspect sensors for damage; replace if threads are damaged or sensor is older than 100k miles.
   ⚠Never apply anti-seize to the sensor body or element. Apply only to the threads as specified.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
3. 3

   Support downpipes
   Place a jack or support stand under each downpipe to support its weight during removal. The V12 downpipes are heavy and awkward to maneuver in the confined space.
   ℹ️On the V12, downpipes run between the cylinder banks and frame rails with very limited clearance.
4. 4

   Remove turbocharger to downpipe flange connection
   Locate the flange connection between each turbocharger outlet and the downpipe inlet. Remove the exhaust flange bolts securing this connection on both left and right sides. Use universal joint extensions to access bolts in tight spaces. If bolts are seized, apply heat carefully around the nut area, avoiding the turbocharger housing.
   ⚠Turbocharger housings are aluminum and can be damaged by excessive heat or force. Work carefully.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
5. 5

   Remove downpipe to mid-pipe flange connection
   Move to the rear flange connection where each downpipe connects to the catalytic converter or mid-pipe section. Remove all flange bolts at this connection point on both sides. These bolts may be more accessible from below.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
6. 6

   Remove exhaust hanger mounts
   Locate the rubber exhaust hangers supporting the downpipes. Remove the hanger bolts or disconnect the hangers from their mounts. Note the exact position of each hanger for proper reinstallation to prevent exhaust vibration.
   Torque spec

   Hanger Bolts27 Nm (20 lb-ft)
7. 7

   Remove downpipes
   With all connections disconnected, carefully maneuver each downpipe out of the engine bay. The V12 configuration requires removing the downpipes at an angle, typically lowering the rear first then rotating forward. Work slowly to avoid damaging surrounding components. Remove left and right downpipes.
   ⚠Watch for contact with coolant hoses, wiring harnesses, and brake lines during removal.
8. 8

   Clean and inspect flange surfaces
   Use a wire brush to thoroughly clean all exhaust flange mating surfaces on the turbocharger outlets and mid-pipe inlets. Remove all old gasket material and carbon buildup. Inspect flanges for warping, cracks, or damage. Check turbocharger outlet flanges for any cracks that could indicate turbocharger problems.
   ℹ️Warped or damaged flanges will cause exhaust leaks regardless of new gaskets.
9. 9

   Prepare new downpipes and sensors
   Install new exhaust flange gaskets on both ends of each new downpipe. Apply anti-seize compound to the threads of both oxygen sensors (threads only, never on the sensor element). If reusing oxygen sensors, inspect threads and clean carefully before applying fresh anti-seize.
   ⚠Anti-seize on oxygen sensor elements will contaminate the sensor and cause failure.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
10. 10

    Install new downpipes
    Carefully maneuver each new downpipe into position, reversing the removal process. Start by positioning the rear connection first, then rotate into position to align with the turbocharger outlet. Ensure gaskets remain properly seated. Support the downpipe with a jack while aligning both flanges.
    ℹ️Do not force downpipes into place. Misalignment indicates improper positioning.
11. 11

    Install turbocharger flange connection
    Apply anti-seize to the threads of the exhaust flange bolts for the turbocharger to downpipe connection. Install bolts hand-tight first, ensuring gasket is properly seated and flanges are flush. Tighten bolts in a cross-pattern to specified torque on both left and right sides.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
12. 12

    Install mid-pipe flange connection
    At the rear flange connection, install new gaskets if not already in place. Install flange bolts and tighten in a cross-pattern to specified torque. Ensure proper gasket compression and flange alignment.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
13. 13

    Reinstall exhaust hangers
    Reconnect all exhaust hangers to their mounting points and install hanger bolts. Tighten to specified torque. Verify that downpipes hang with proper clearance from surrounding components and do not contact the chassis, driveshaft, or suspension.
    Torque spec

    Hanger Bolts27 Nm (20 lb-ft)
14. 14

    Install oxygen sensors
    Thread each oxygen sensor into its bung on the downpipe by hand, ensuring threads engage properly without cross-threading. Once hand-tight, use the oxygen sensor socket to tighten to specified torque. Connect oxygen sensor electrical connectors, ensuring they click securely into place.
    ⚠Cross-threading oxygen sensors will damage the downpipe bung. Thread carefully by hand first.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
15. 15

    Reinstall heat shields and covers
    Reinstall all heat shields in their original positions, ensuring proper clearance from moving parts and hot exhaust components. Install heat shield bolts and tighten to specified torque. Reinstall engine undercover panels and any mounting bolts removed during preparation.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)

    Mounting Bolts37 Nm (27 lb-ft)

Reassembly

1. Reconnect negative battery terminal.
2. Perform a visual inspection from below to verify all connections are secure and no tools or parts were left in the engine bay.
3. Lower vehicle to the ground.
4. Clear any diagnostic trouble codes related to oxygen sensor disconnection using a scan tool if available.

Verification

• Start engine and allow to idle. Listen for any exhaust leaks at flange connections, which will present as a ticking or hissing sound.
• Rev engine to 2500-3000 RPM while stationary and listen for leaks under load.
• Verify no check engine light appears for oxygen sensor faults after a brief test drive.
• Perform a test drive including moderate acceleration to verify proper exhaust flow and turbocharger operation.
• After test drive, raise vehicle and inspect all flange connections for signs of exhaust leaks (soot marks).
• Verify oxygen sensor connectors remain securely attached and wiring has proper clearance from hot exhaust components.
• Check exhaust hanger positions to ensure no contact with chassis or driveline components during engine movement.

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