Here’s a description of the Mercedes-Benz W221 S-Class (3.5L V6 M272 engine) exhaust catalytic system:

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Exhaust Catalytic Converter Description – W221 3.5 V6 (M272)

Vehicle: Mercedes-Benz W221 S-Class

Engine: M272 E35 – 3.5L V6, naturally aspirated

Years: Approx. 2005–2013 (varies by market)

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System Overview

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The W221 with the M272 engine uses a dual catalytic converter setup integrated into its exhaust manifolds and mid-pipes. These components are designed to reduce harmful emissions and comply with Euro 4/5 standards (depending on year and region).

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Key Components

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1. Exhaust Manifolds with Pre-Catalytic Converters:
   
• Located directly on each cylinder bank (V6 layout – 2 banks).
• Each manifold contains a small pre-cat (warm-up catalyst) to quickly treat gases upon cold start.
• Cast stainless steel with integrated oxygen sensor ports.
2. 
   
3. Main Catalytic Converters (Primary Cats):
   
• Located in the mid-pipe section, downstream of the manifolds.
• High-capacity ceramic or metallic substrate coated with precious metals (Platinum, Rhodium, Palladium).
• Reduces NOx, CO, and hydrocarbons significantly.
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5. Oxygen Sensors:
   
• 4 sensors total (2 upstream, 2 downstream).
• Upstream sensors control air-fuel ratio.
• Downstream sensors monitor catalyst efficiency.
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⚠️ Common Issues:

• Catalyst inefficiency codes (P0420/P0430) due to aging or internal substrate damage.
• Rattling sounds if the substrate breaks loose.
• Increased fuel consumption if oxygen sensors or catalysts fail.

🧰 Replacement Notes:

• OEM catalytic converters are expensive due to precious metal content.
• Aftermarket options or cat-delete pipes are sometimes used, but may trigger CEL and fail emissions.
• Must be welded or flanged properly for secure fitment.

Let me know if you need part numbers, diagrams, or downpipe details too.