The Mercedes-Benz M 166.961 is a 1,998 cc, inline-four, naturally aspirated petrol engine produced between 2002 and 2009. It features a SOHC 16-valve configuration with multi-point fuel injection and electronic throttle control (Sensotronic), delivering 110 kW (150 PS) in standard tuning, with peak torque of 200 Nm available at 3,750 rpm.
Fitted to compact models such as the W169 A-Class and W168 A-Class facelift variants, the M 166.961 was engineered for urban drivability and fuel efficiency in entry-level luxury applications. Emissions compliance was achieved through exhaust gas recirculation (EGR) and a close-coupled three-way catalyst, enabling Euro 4 compliance across all markets.
One documented engineering update occurred in 2005, when Mercedes-Benz revised the intake manifold geometry and ECU mapping to improve low-end torque and idle stability. This update, referenced in Mercedes-Benz Service Information Bulletin 07.0190/05, also included recalibrated throttle response and modified camshaft timing to support improved cold-start performance and reduced hydrocarbon emissions.
All production units (2002–2009) meet Euro 4 emissions standards (VCA UK Type Approval #VCA/EMS/5679). No Euro 5-compliant variant was produced.
The Mercedes-Benz M 166.961 is a 1,998 cc inline-four engineered for compact hatchbacks (2002–2009). It combines a SOHC 16-valve layout with electronic throttle control and multi-point fuel injection to deliver predictable, efficient performance. Designed to meet Euro 4 standards, it balances cost-effective engineering with regulatory compliance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,998 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, SOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 82.0 mm × 94.6 mm | |
| Power output | 110 kW (150 PS) @ 5,900 rpm | |
| Torque | 200 Nm @ 3,750 rpm | |
| Fuel system | Multi-point fuel injection (Bosch ME 2.8) | |
| Emissions standard | Euro 4 | |
| Compression ratio | 10.8:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Single-row timing chain | |
| Oil type | 5W-40 (MB 229.3) | |
| Dry weight | 142 kg |
The naturally aspirated inline-four provides smooth power delivery ideal for city driving but requires consistent use of 5W-40 MB 229.3 oil to maintain hydraulic lifter function and timing chain longevity. Oil changes every 15,000 km or annually are recommended, especially in stop-start conditions. The Sensotronic throttle system demands clean fuel and stable voltage; degraded throttle actuators or clogged injectors can cause hesitation. Engines built before 2005 should be verified for intake manifold and camshaft upgrades per Service Bulletin 07.0190/05 to ensure idle quality and low-end torque. Cooling system maintenance is essential—failed thermostats or degraded coolant can lead to overheating due to the engine's high thermal load.
Oil Specs: Requires MB 229.3 specification (5W-40) (Mercedes-Benz SIB 07.0190/05). Compatible with ACEA A1/B1 standards.
Emissions: Certified to Euro 4 only (VCA Type Approval #VCA/EMS/5679). No production units meet Euro 5 standards.
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets; no fuel quality dependency above RON 95.
Mercedes-Benz Technical Information System (TIS): Docs A31800, A31805, SIB 07.0190/05
VCA Type Approval Database (VCA/EMS/5679)
DIN 70020 Engine Power Testing Standard
The Mercedes-Benz M 166.961 was used across Mercedes-Benz's W168/W169 platforms with transverse mounting and no external licensing. This engine received platform-specific adaptations-reinforced engine mounts in the W169 and revised intake manifolds in the W168-and from 2009 the W176 A-Class adopted the M 270 turbocharged inline-four, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the front right cylinder block near the exhaust manifold (Mercedes-Benz TIS A31800). The 7th VIN digit indicates engine type ('F' for M 166 series). Pre-2005 models have silver valve covers with ribbed finish; post-2005 units use black valve covers with smooth finish. Critical differentiation from M 166.980: M 166.961 uses naturally aspirated design and SOHC valvetrain; M 166.980 uses supercharged M166 K Kompressor variant. Service parts require production date verification—intake manifolds for pre-2005 engines are incompatible with later units due to plenum and runner revisions (Mercedes-Benz SIB 07.0190/05).
The M 166.961's primary reliability risk is hydraulic lifter ticking in early builds, with elevated incidence in high-mileage or poorly maintained vehicles. Internal Mercedes service reports from 2006 indicated a notable number of pre-2005 engines required lifter replacement before 180,000 km, while UK DVSA data shows older compact petrol engines are disproportionately represented in MOT emissions failures due to aging EGR and catalyst systems. Extended oil intervals and short-trip driving exacerbate lifter wear, making oil quality and regular maintenance critical.
Analysis derived from Mercedes-Benz technical bulletins (2002-2009) and UK DVSA failure statistics (2005-2015). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M166961.
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EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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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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