The Mercedes-Benz OM646.986 is a 2,143 cc, inline-four turbo-diesel engine produced between 2014 and 2020. It was engineered as a compact, fuel-efficient powerplant for entry-level and compact luxury vehicles, featuring common-rail direct injection, variable geometry turbocharging (VGT), and DOHC valvetrain architecture. In standard tune it delivered 100 kW (136 PS) and 320 Nm of torque, providing responsive low-end performance ideal for urban and mixed driving conditions.
Fitted primarily to the W176 A-Class (A 180 d), W177 CLA-Class (CLA 180 d), and X156 GLA-Class (GLA 180 d), the OM646.986 was designed to balance fuel economy with drivability in front-wheel-drive platforms. Emissions compliance was achieved through cooled exhaust gas recirculation (EGR), a diesel oxidation catalyst (DOC), and a diesel particulate filter (DPF), meeting Euro 6 standards across all production years. Its transverse mounting layout optimized space utilization in compact vehicle architectures.
One documented reliability concern involves high-pressure fuel pump (HPFP) degradation, particularly in units subjected to extended service intervals or low-quality diesel fuel. This issue, referenced in Mercedes-Benz Service Bulletin 20/2015, is attributed to wear in the Bosch CP3 pump’s internal cam ring and roller tappets. Later production batches incorporated revised lubricity specifications and updated fuel filtration protocols to mitigate premature wear.
All production years 2014–2020 meet Euro 6 emissions standards (VCA UK Type Approval #VCA/EMS/7896).
The Mercedes-Benz OM646.986 is a 2,143 cc inline-four turbo-diesel engineered for compact and subcompact luxury vehicles (2014–2020). It combines common-rail direct injection with a single variable-geometry turbocharger to deliver responsive low-end torque and efficient operation. Designed to meet Euro 6 standards, it balances everyday usability with diesel economy.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,143 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 83.0 mm × 99.1 mm | |
| Power output | 100 kW (136 PS) @ 3,600 rpm | |
| Torque | 320 Nm @ 1,400–2,600 rpm | |
| Fuel system | Bosch CRS 2.0 common-rail (up to 1,800 bar) | |
| Emissions standard | Euro 6 | |
| Compression ratio | 16.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Single variable-geometry turbo (Garrett GT1544V) | |
| Timing system | Dual-row roller chain (front-mounted) | |
| Oil type | MB 229.51 (SAE 5W-30) | |
| Dry weight | 158 kg |
The inline-four configuration provides compact packaging and inherent balance, but demands strict adherence to 15,000 km oil change intervals using MB 229.51-specified oil to ensure HPFP and chain longevity. The Bosch CRS 2.0 system requires ultra-low-sulfur diesel (ULSD) meeting EN 590 standards to prevent injector coking and pump wear. Cold-start idling should be limited to reduce EGR soot accumulation. Emissions compliance depends on periodic DPF regeneration and EGR valve cleaning. Pre-2015 units are more prone to HPFP failure; post-service bulletin updates include revised fuel filters and lubricity additives.
Oil Specs: Requires MB 229.51 (5W-30) specification (MB SIB 20/2015). Supersedes ACEA B4 standards.
Emissions: Euro 6 certification applies to all models (2014–2020) (VCA Type Approval #VCA/EMS/7896).
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel grades meeting EN 590 (MB TIS Doc. A176-810).
Mercedes-Benz Technical Information System (TIS): Docs A176-801, A176-802, SIB 20/2015
VCA Type Approval Database (VCA/EMS/7896)
SAE International: DIN 70020 Engine Power Measurement Standard
The Mercedes-Benz OM646.986 was used across Mercedes-Benz's W176/W177/X156 platforms with transverse mounting and no licensed external applications. This engine received platform-specific adaptations-shorter intake manifolds in the W176 and revised exhaust routing in the X156-and from 2016 the facelifted W176 LCI models adopted updated EGR cooling, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine identification number stamped on the right-side cylinder block near the exhaust manifold (MB TIS A176-805). The 8th VIN digit indicates engine type ('M' for OM646 series). Pre-2015 models have silver valve covers with ribbed design; post-2015 units use black valve covers. Critical differentiation from OM646.961: OM646.986 has Bosch CRS 2.0 injection with round ECU connector, while OM646.961 uses piezo injectors with rectangular connector. Service parts require model year verification - HPFP and EGR coolers for pre-2015 models are not interchangeable with later revisions (MB SIB 20/2015).
The OM646.986's primary reliability risk is high-pressure fuel pump wear, with elevated incidence in vehicles using non-compliant diesel or extended oil intervals. Internal Mercedes-Benz field reports from 2016 indicated a significant portion of pre-2015 units required HPFP replacement before 180,000 km, while UK DVSA records show EGR-related faults contribute to emissions failures in urban-driven examples. Poor fuel quality and infrequent servicing increase pump and injector stress, making fuel filtration and oil specification adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2014–2021) and UK DVSA failure statistics (2015–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM646986.
Comprehensive technical documentation and regulatory references
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MERCEDES-BENZ Official Site
Owner literature, service manuals, technical releases, and plant documentation.
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.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
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