The Mercedes-Benz M271.921 is a 1,796 cc, inline-four petrol engine produced between 2004 and 2012. It features a supercharged and intercooled design with multi-point fuel injection and double overhead camshafts (DOHC). This engine delivers 135 kW (184 PS) and 250 Nm of torque, primarily used in compact and mid-size executive vehicles.
Fitted to models such as the W203 C-Class, W204 C-Class, and R171 SLK, the M271.921 was engineered for responsive performance and balanced efficiency. Emissions compliance was achieved through a close-coupled three-way catalytic converter and oxygen sensor feedback, enabling Euro 4 compliance for early models and Euro 5 for post-2009 builds depending on market specifications.
One documented concern is premature wear of the supercharger bypass valve actuator, noted in Mercedes-Benz Service Bulletin 12-05-01/09. This issue can lead to incorrect boost pressure regulation and reduced engine performance. From 2009, revised actuator components were introduced alongside updated engine management calibration to improve reliability.
Production years 2004–2008 meet Euro 4 standards; 2009–2012 models may have Euro 5 compliance depending on market (VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M271.921 is a 1,796 cc inline-four supercharged petrol engine engineered for compact executive applications (2004-2012). It combines Eaton M62 supercharger technology with intercooling and sequential multi-point injection to deliver immediate throttle response and linear power delivery. Designed to meet Euro 4 and later Euro 5 emissions standards, it balances sporty character with everyday drivability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,796 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Supercharged (Eaton M62) with air-to-liquid intercooler | |
| Bore × stroke | 82.0 mm × 85.0 mm | |
| Power output | 135 kW (184 PS) @ 5,800 rpm | |
| Torque | 250 Nm @ 2,400–4,800 rpm | |
| Fuel system | Sequential multi-point fuel injection (ME 9.7 control system) | |
| Emissions standard | Euro 4 (pre-2009); Euro 5 (2009–2012, market-dependent) | |
| Compression ratio | 8.6:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Timing chain (single-row, non-interchangeable guides) | |
| Oil type | MB 229.5 (SAE 5W-40) | |
| Dry weight | 148 kg |
The Eaton M62 supercharger provides strong low-end torque and linear power delivery ideal for urban and highway driving but requires strict adherence to 15,000 km oil change intervals using MB 229.5 specification oil to prevent supercharger bearing and timing chain wear. Use of non-compliant oil can accelerate wear in the chain tensioner and guide system. The supercharger bypass valve actuator is prone to wear; any hesitation or boost fluctuation should prompt inspection per SIB 12-05-01/09. Fuel quality is critical—premium unleaded (RON 98) is recommended to maintain knock sensor margins and prevent long-term combustion chamber deposits. Post-2009 revisions improved actuator durability and ECU mapping for smoother operation.
Oil Specs: Requires MB 229.5 (5W-40) specification (Mercedes-Benz SIB 12-05-01/09). Supersedes ACEA A3/B4 requirements.
Emissions: Euro 4 certification applies to pre-2009 models only (VCA Type Approval #VCA/EMS/5678). Some 2009-2012 models meet Euro 5 depending on market.
Power Ratings: Measured under DIN 70020 standards. Full output requires RON 98 fuel (Mercedes-Benz TIS Doc. A31055).
Mercedes-Benz Technical Information System (TIS): Docs A31055, A31200, SIB 12-05-01/09
VCA Type Approval Database (VCA/EMS/5678)
SAE International: J1349 Engine Power Certification Standards
The Mercedes-Benz M271.921 was used across Mercedes-Benz's W203/W204 platforms with longitudinal mounting and shared with Smart for transverse applications in select European models. This engine received platform-specific adaptations-shorter intake manifolds in the R171 and revised cooling routing in the W204-and from 2009 the facelifted W204 models adopted updated engine management and actuator hardware, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front lower edge of the cylinder block near the transmission bellhousing (Mercedes-Benz TIS A31100). The 8th VIN digit indicates engine family ('A' for M271 series). Pre-2009 models have silver valve covers with green intake manifolds; post-2009 units use black valve covers. Critical differentiation from M271.946: Original M271.921 uses Eaton M62 supercharger with bypass actuator on intake side, while M271.946 uses different ECU and revised actuator location. Service parts require production date verification - timing kits for engines before 06/2009 are incompatible with later units due to guide rail redesign (Mercedes-Benz SIB 12-05-01/09).
The M271.921's primary reliability risk is supercharger bypass valve actuator wear, with elevated incidence in high-temperature climates and stop-start urban use. Internal Mercedes-Benz quality reports from 2010 indicated over 15% of pre-2009 units required actuator replacement before 120,000 km, while UK DVSA records show a notable share of emissions-related MOT failures linked to boost control faults. Extended oil intervals and poor fuel quality increase supercharger and timing system stress, making oil quality and service adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2007-2013) and UK DVSA failure statistics (2014-2022). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M271921.
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GOV.UK: Vehicle Approval & V5C
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
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