The Mercedes-Benz OM642.856 is a 2,987 cc, V6 turbo-diesel engine produced between 2006 and 2018. It features common-rail direct injection, variable geometry turbocharging (VGT), and DOHC 24-valve configuration. In standard output, it delivers 165 kW (224 PS) and 540 Nm of torque, with applications across executive sedans and luxury SUVs.
Fitted to models such as the W211 E-Class, W221 S-Class, and W164 ML-Class, the OM642.856 was engineered for balanced performance, refinement, and fuel efficiency. Emissions compliance was achieved via exhaust gas recirculation (EGR), diesel particulate filter (DPF), and selective catalytic reduction (SCR) with AdBlue injection, enabling Euro 4 through Euro 6 certification depending on model year and market.
One documented reliability concern is premature high-pressure fuel pump (HPFP) wear, particularly in early builds. This issue, highlighted in Mercedes-Benz Service Bulletin 20/2009, is linked to fuel contamination and marginal filtration in sustained high-load operation. From 2010 onward, revised Bosch CP4-based fuel systems with enhanced filtration were implemented to improve durability.
Production years 2006–2009 meet Euro 4 standards; 2010–2013 models comply with Euro 5; 2014–2018 variants achieve Euro 6 compliance depending on market (VCA UK Type Approval #VCA/EMS/5680).
The Mercedes-Benz OM642.856 is a 2,987 cc V6 turbo-diesel engineered for executive and SUV applications (2006–2018). It combines common-rail direct injection with a variable-geometry turbocharger to deliver responsive power and strong low-end torque. Designed to meet Euro 4 through Euro 6 emissions standards, it balances performance with efficiency and long-distance refinement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,987 cc | |
| Fuel type | Diesel | |
| Configuration | V6, DOHC, 24-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 88.0 mm × 82.1 mm | |
| Power output | 165 kW (224 PS) @ 3,600 rpm | |
| Torque | 540 Nm @ 1,600–2,400 rpm | |
| Fuel system | Bosch CRS 3.0 common-rail (up to 1,800 bar) | |
| Emissions standard | Euro 4 (2006–2009); Euro 5 (2010–2013); Euro 6 (2014–2018) | |
| Compression ratio | 16.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Single variable-geometry turbo (Garrett GT1749V) | |
| Timing system | Dual chain (front-mounted, robust design) | |
| Oil type | MB 229.5 (SAE 5W-30) | |
| Dry weight | 196 kg |
The V6 configuration provides smooth, linear power delivery ideal for highway cruising but demands strict adherence to 15,000 km oil change intervals using MB 229.5 specification oil to maintain turbo and HPFP longevity. Use of ultra-low-sulfur diesel (EN 590) is critical to prevent injector and fuel pump wear. Cold starts should be brief; prolonged idling increases EGR and DPF soot loading. Post-2010 models benefit from upgraded CP4 fuel pumps and enhanced filtration. EGR, DPF, and SCR systems require periodic regeneration and cleaning to prevent limp mode. Timing chains are generally durable but inspection is recommended beyond 200,000 km. AdBlue system maintenance is essential for Euro 5+ compliance.
Oil Specs: Requires MB 229.5 specification (Mercedes-Benz SIB 22/2007). Not compatible with ACEA A/B standards.
Emissions: Euro 4 applies to 2006–2009 models. Euro 5 confirmed for 2010–2013. Euro 6 compliance for 2014–2018 models in EU markets (VCA Type Approval #VCA/EMS/5680).
Power Ratings: Measured under DIN 70020. Output maintained across EU and North American variants (Mercedes-Benz TIS Doc. M13512).
Mercedes-Benz Technical Information System (TIS): Docs M12682, M13144, SIB 20/2009, SIB 22/2007
VCA Type Approval Database (VCA/EMS/5680)
ISO 1585:1996 Road vehicles — Test code for net power of internal combustion engines
The Mercedes-Benz OM642.856 was used across Mercedes-Benz's W211/W221/W164 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-reinforced engine mounts in the W164 and revised cooling circuits in the W221-and from 2010 the updated W211 facelift adopted the OM642.956 variant with CP4 fuel system revisions, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front of the cylinder block near the timing cover (Mercedes-Benz TIS M12892). The 8th VIN digit indicates engine type ('6' for OM642 series). Pre-2010 models have silver valve covers with ribbed plastic covers; post-2010 units use black valve covers. Critical differentiation from OM642.956: Original .856 uses Bosch CP3 HPFP with circular fuel filter housing, while .956 uses CP4 with rectangular housing. Service parts require production date verification - fuel pumps and injectors before 06/2010 are not compatible with later units due to CP4 system integration (Mercedes-Benz SIB 20/2009).
The OM642.856's primary reliability risk is high-pressure fuel pump degradation, with elevated incidence in high-mileage and mixed-use conditions. Internal Mercedes quality reports from 2011 indicated a notable frequency of CP3 pump failures before 180,000 km in non-EU fuel markets, while UK DVSA data links EGR-related faults to urban-driven units. Extended idling and poor fuel quality increase HPFP and injector stress, making fuel filtration and oil interval adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2007-2015) and UK DVSA failure statistics (2012-2020). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM642856.
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MERCEDES-BENZ Official Site
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
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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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