Flex Pipe

Replace the exhaust flex pipe on the 2007-2013 Mercedes-Benz S65 AMG M275 6.0L V12 BiTurbo engine to eliminate exhaust leaks and restore proper exhaust system flexibility.

Warnings

Tools required

Parts

• Exhaust flex pipe assembly × 1 — Use OEM specification
• Exhaust flange gaskets × 2 — Use OEM specification
• Exhaust flange bolts/nuts (if corroded) × 6 — M10 exhaust hardware
• Oxygen sensor (if damaged during removal) × 1 — Use OEM specification

Preparation

1. Ensure engine and exhaust system are completely cool to the touch
2. Raise vehicle on lift or secure on jack stands at appropriate lift points
3. Spray all exhaust fasteners with penetrating oil and allow to soak for at least 30 minutes
4. Locate the flex pipe section on the affected exhaust bank between the catalytic converter and center muffler section
5. Identify all oxygen sensors in the work area and plan removal strategy

Procedure

1. 1

   Remove heat shields and covers
   Remove any heat shields or protective covers that block access to the flex pipe. These are typically held by 10mm or 13mm screws. Set aside covers and hardware for reinstallation.
   Torque spec

   Cover Screws15 Nm (11 lb-ft)
2. 2

   Disconnect oxygen sensor
   Disconnect the electrical connector for the oxygen sensor located near the flex pipe. Using a 22mm O2 sensor socket, carefully remove the oxygen sensor from the exhaust pipe. Turn counterclockwise and support the sensor to prevent wire damage. Inspect threads and replace sensor if damaged.
   ⚠Do not allow the O2 sensor to hang by its wiring. Support the sensor and secure it away from the work area.
   Torque spec

   O2 Sensor64 Nm (47 lb-ft)
3. 3

   Support exhaust system
   Place an adjustable jack or exhaust support stand under the exhaust section containing the flex pipe to support its weight during removal. Position the support just aft of the flex pipe section to prevent the exhaust from dropping.
   ⚠The exhaust section is heavy. Ensure support is stable before loosening any fasteners.
4. 4

   Disconnect exhaust hangers
   Locate the rubber exhaust hangers supporting the affected exhaust section. Use a pry bar or exhaust hanger tool to disconnect the hangers from their mounting points. Work carefully to avoid tearing the rubber hangers if they are to be reused.
   Torque spec

   Hanger Bolts27 Nm (20 lb-ft)
5. 5

   Remove forward flange connection
   Locate the forward flange connection at the front of the flex pipe (typically at the catalytic converter outlet). Remove the flange bolts using a 17mm socket. There are usually 3 bolts per flange. Remove the old gasket and inspect the flange face for damage.
   ⚠Bolts may be severely corroded. Apply heat if necessary but be aware of nearby components. Have replacement hardware available.
   Torque spec

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

   Remove rear flange connection
   Locate the rear flange connection at the back of the flex pipe section. Remove the flange bolts using a 17mm socket. Separate the flanges and remove the old gasket. Lower the exhaust section slightly using the support jack to create clearance.
   Torque spec

   Flange Bolts45 Nm (33 lb-ft)
7. 7

   Remove flex pipe assembly
   With both flanges disconnected and hangers released, carefully maneuver the flex pipe section out from under the vehicle. Note the orientation and routing for proper installation of the replacement part. Inspect the removed flex pipe for failure mode (cracks, internal collapse, or separation).
   ℹ️Mark or photograph the exact position of hangers and routing before complete removal to aid in proper reinstallation.
8. 8

   Clean flange surfaces
   Use a wire brush to thoroughly clean both exhaust flange mating surfaces on the catalytic converter outlet and the center pipe inlet. Remove all old gasket material, carbon deposits, and corrosion to ensure a proper seal. Wipe clean with shop towels.
   ℹ️Proper flange surface preparation is critical to prevent exhaust leaks after reassembly.
9. 9

   Position new flex pipe
   Install new flange gaskets on both connection points. Position the new flex pipe assembly under the vehicle, aligning it with the forward and rear flange connections. Use the support jack to hold the assembly at the correct height and angle. Verify proper routing and clearance from heat-sensitive components.
   ℹ️Ensure the flex pipe is not twisted or binding. The corrugated section should be free to flex without restriction.
10. 10

    Install flange fasteners
    Install the flange bolts at both the forward and rear connections. Start all bolts by hand to ensure proper thread engagement. Apply a small amount of anti-seize to bolt threads if available. Tighten bolts in a cross pattern to ensure even compression of the gasket.
    ⚠Do not fully torque fasteners until all bolts are started and hangers are connected. This allows for alignment adjustment.
    Torque spec

    Flange Bolts45 Nm (33 lb-ft)
11. 11

    Reconnect exhaust hangers
    Reconnect the rubber exhaust hangers to their mounting points. Use a pry bar or hanger tool to stretch the rubber mounts onto the support hooks. Ensure the exhaust is properly positioned with adequate clearance from the underbody, fuel lines, and other components.
    Torque spec

    Hanger Bolts27 Nm (20 lb-ft)
12. 12

    Torque all fasteners
    With the exhaust properly positioned and supported by hangers, torque all flange bolts to specification in a cross pattern. Verify that the exhaust system sits level and has proper clearance throughout its length. Remove the support jack.
    Torque spec

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

    Reinstall oxygen sensor
    Apply a small amount of anti-seize compound to the oxygen sensor threads (avoid contaminating the sensor tip). Thread the O2 sensor into the exhaust pipe by hand, then torque to specification using the 22mm O2 sensor socket. Reconnect the electrical connector and ensure the wiring is properly routed away from hot exhaust components.
    ⚠Use minimal anti-seize on O2 sensor threads. Excess compound can contaminate the sensor and cause false readings.
    Torque spec

    O2 Sensor64 Nm (47 lb-ft)
14. 14

    Reinstall heat shields
    Reinstall all heat shields and protective covers removed during disassembly. Ensure shields are properly positioned and not contacting the exhaust pipe. Torque all mounting screws to specification.
    Torque spec

    Cover Screws15 Nm (11 lb-ft)

Reassembly

1. Verify all exhaust hangers are properly engaged and the system has adequate clearance from the underbody
2. Ensure all electrical connectors for oxygen sensors are fully seated and secured
3. Double-check that all flange bolts are torqued to specification and gaskets are properly seated
4. Confirm heat shields are securely mounted and not rattling or contacting exhaust components

Verification

• Lower vehicle and start engine, allowing it to idle
• Listen for exhaust leaks at both flange connections and around the flex pipe area
• Check for visible exhaust smoke or fumes escaping from joints
• Rev engine to 2500-3000 RPM and verify no exhaust leaks under load
• Visually inspect the new flex pipe for proper positioning and adequate clearance during engine movement
• Test drive vehicle and verify no exhaust drone, rattles, or unusual noises
• After initial test drive, recheck all flange bolts for proper torque when exhaust has cooled
• Verify no Check Engine Light or O2 sensor fault codes using diagnostic scanner

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