Intermediate Pipe

Replace the intermediate pipe (center exhaust section) on a 2019 Mercedes-Benz G-Class 4.0L Turbo V8, including oxygen sensor transfer, flange disconnection, and hanger removal.

Warnings

Tools required

Parts

• Intermediate exhaust pipe assembly × 1 — Use OEM specification or approved aftermarket
• Exhaust flange gasket (front connection) × 1 — Mercedes part number A0004920980 or equivalent
• Exhaust flange gasket (rear connection) × 1 — Mercedes part number A0004920980 or equivalent
• Flange bolts/nuts (if corroded) × 6 — M10x1.5 flange bolts, replace as needed

Preparation

1. Ensure vehicle has been parked and engine fully cooled for at least 1 hour
2. Park vehicle on level surface and engage parking brake
3. Raise vehicle on lift or secure on jack stands at all four corners to manufacturer-specified lift points
4. Verify vehicle is stable and will not shift during undercarriage work
5. Spray all exhaust flange bolts and hanger mounting points with penetrating oil, allow to soak minimum 30 minutes
6. Locate intermediate pipe: runs from catalytic converter outlet flanges (near transmission tunnel) rearward to connection point ahead of muffler assembly

Procedure

1. 1

   Disconnect oxygen sensor electrical connector
   Locate the downstream oxygen sensor(s) mounted in the intermediate pipe. Trace wiring harness upward to electrical connector (typically clipped to heat shield or chassis bracket). Press release tab and disconnect connector. Unclip wiring from any retaining clips along the intermediate pipe to allow pipe removal without damaging sensor harness.
2. 2

   Remove downstream oxygen sensor from intermediate pipe
   Using oxygen sensor socket, carefully remove the downstream oxygen sensor from the intermediate pipe. Turn counterclockwise to remove. If sensor is seized, apply additional penetrating oil around threads and allow to soak, then retry with steady pressure (avoid shocking or hammering which can damage sensor). Once removed, set sensor aside in clean area where tip will not be damaged or contaminated.
   ⚠Do not allow oxygen sensor tip to contact ground, oil, or other contaminants. Do not drop sensor. Contamination or impact damage will require sensor replacement.
3. 3

   Remove front flange connection bolts
   Locate the front flange connection where intermediate pipe bolts to the catalytic converter outlet pipes. This is a spring-loaded flange connection on each side (left and right banks); verify the exact bolt/nut count per bank against factory documentation before ordering fasteners. Using appropriate Torx or hex socket, remove all 6 flange bolts/nuts. If bolts are severely corroded or rounded, use penetrating oil and allow additional soak time or apply heat carefully with propane torch if necessary. Support intermediate pipe weight by hand or with transmission jack once fasteners are loosened.
4. 4

   Remove rear flange connection bolts
   Move to rear flange connection where intermediate pipe connects to rear exhaust section (muffler inlet pipe). Verify the exact rear flange configuration and bolt count against factory documentation before removal. Remove all 3 bolts using appropriate socket. Keep intermediate pipe supported to prevent it from dropping once fasteners are removed.
5. 5

   Disconnect exhaust hangers
   The intermediate pipe is suspended by rubber exhaust hangers mounted to chassis brackets. Locate the hanger mounting points along the intermediate pipe (typically 2-3 hanger tabs welded to pipe). Using exhaust hanger removal tool or pry bar, compress/stretch rubber hangers and work hanger tabs out of rubber insulators. Work methodically from front to rear, keeping pipe supported as hangers are released.
   ⚠Rubber exhaust hangers are under tension and can snap back when released. Keep hands clear of snap-back path.
6. 6

   Remove intermediate pipe from vehicle
   With all flange bolts and hangers disconnected, carefully lower and maneuver intermediate pipe out from under vehicle. The pipe may need to be rotated or angled to clear frame rails, axles, and driveshaft. Work slowly to avoid damaging brake lines, fuel lines, or other undercarriage components. Once clear, remove pipe from under vehicle.
7. 7

   Clean flange surfaces and inspect connection points
   Using wire brush, thoroughly clean both front and rear flange mating surfaces on catalytic converters and rear exhaust section. Remove all traces of old gasket material, carbon deposits, and corrosion to ensure proper seal with new gaskets. Inspect flange surfaces for warping, cracks, or damage that could prevent proper sealing. Inspect rubber exhaust hanger insulators on chassis brackets for tears, deterioration, or excessive wear; replace if damaged.
8. 8

   Install oxygen sensor in new intermediate pipe
   Apply thin coat of nickel-based anti-seize compound to oxygen sensor threads (avoid getting anti-seize on sensor tip). Thread sensor by hand into intermediate pipe boss until snug, then torque to specification using oxygen sensor socket. Ensure sensor wiring routing will not interfere with installation or contact hot exhaust components.
   ⚠Do not over-torque oxygen sensor. Excessive torque can damage sensor threads in pipe boss or crack sensor body.
   Torque spec

   O2 Sensor55 Nm (40 lb-ft)
9. 9

   Position new intermediate pipe and engage exhaust hangers
   Lift new intermediate pipe into position under vehicle, aligning with front and rear flange connections. Before bolting flanges, install pipe hanger tabs into rubber insulators on chassis brackets. Use pry bar or exhaust hanger tool to stretch rubber insulators as needed to engage hanger tabs. Verify pipe alignment allows flanges to mate properly without binding.
10. 10

    Install new gaskets and connect front flange
    Position new exhaust flange gaskets at front connection point (one gasket for each bank, left and right). Align intermediate pipe flange to catalytic converter outlet flanges. Install all 6 flange bolts and start by hand to ensure proper thread engagement. Tighten bolts in star/cross pattern to ensure even gasket compression. Torque all bolts to the manufacturer-specified value for the spring-loaded flange (confirm spec and whether bolts seat by spring compression rather than fixed torque).
11. 11

    Install new gasket and connect rear flange
    Position new exhaust flange gasket at rear connection point. Align intermediate pipe rear flange to muffler inlet flange. Install all 3 flange bolts and start by hand. Tighten bolts in triangular pattern for even gasket compression. Torque all bolts to specification in two stages: first to 50% of final torque, then to full specification.
12. 12

    Reconnect oxygen sensor electrical connector
    Route oxygen sensor wiring harness away from hot exhaust surfaces and moving components. Secure wiring in original retaining clips along pipe or chassis. Connect oxygen sensor electrical connector to vehicle harness, ensuring connector locks fully with audible click. Verify connector seal is properly seated to prevent moisture intrusion.
13. 13

    Final inspection and clearance verification
    Visually inspect all flange connections to verify bolts are fully torqued and gaskets are properly seated with no gaps. Verify exhaust hangers are fully engaged in rubber insulators. Check clearance between intermediate pipe and all surrounding components (frame rails, driveshaft, axles, fuel tank, brake lines) throughout full suspension travel range by manually pushing up/down on pipe. Ensure adequate clearance to all surrounding components per factory specification, with no contact throughout full suspension travel.

Reassembly

1. Lower vehicle from lift or jack stands
2. Start engine and allow to reach operating temperature while listening for exhaust leaks at front and rear flange connections
3. If any exhaust leaks are detected (hissing sound, visible exhaust gases), shut down engine, allow to cool, and re-torque affected flange bolts
4. Clear any diagnostic trouble codes (DTCs) related to oxygen sensors using scan tool if check engine light is illuminated

Verification

• With engine at idle, walk around vehicle and listen carefully for exhaust leaks at all flange connections - no hissing or ticking sounds should be present
• Verify no rattling or contact noises from intermediate pipe during idle, indicating proper hanger engagement and clearance
• Rev engine to 2500-3000 RPM and verify no exhaust leaks become apparent under increased exhaust flow
• Take vehicle for test drive and verify normal exhaust tone with no unusual vibrations or rattles
• After test drive, inspect all flange connections for signs of leakage (black soot deposits around flanges indicate leak)
• Using scan tool, verify oxygen sensor is providing valid readings and no exhaust-related DTCs are present

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