Mercedes-Benz OM656.929 Engine Overview

The OM656.929 is a specific variant of the Mercedes-Benz OM656 series 3.0T inline-six diesel engine. It represents Mercedes’ next-generation modular engine, known for its powerful performance (S 400 d version delivers up to 340 hp / 700 Nm), high efficiency, smooth operation, and compliance with strict emission standards (such as SCR technology). This engine is widely used across various mid-to-high-end Mercedes-Benz models, including W222 S 400 d, GLE 350 d, E 350 d, and more, making it one of the most powerful production diesel engines currently offered by Mercedes-Benz.

Key Features:

1. Inline-six design: Inheriting the excellent characteristics of Mercedes straight-six engines, offering smooth operation.
2. Advanced emission technology: Equipped with SCR (Selective Catalytic Reduction) to reduce NOx emissions, meeting the latest Euro 6d emission standards.
3. High power output: The 400 d version delivers 250 kW (340 hp) and 700 Nm peak torque, providing strong performance.
4. Low fuel consumption: Despite high power, it delivers excellent fuel efficiency.
5. Wide application: Used in multiple Mercedes-Benz models, including S-Class, E-Class, G-Class, GLE, GLS, and CLS, with different power variants such as 350 d and 400 d.

Example Vehicle Applications:

1. S 400 d (W222)
2. E 350 d (W213)
3. G 350 d (W463)
4. GLE 350 d (V167)

The OM656.929 engine represents Mercedes-Benz’s focus on combining high performance with environmental compliance.

Upgrade from OM651 Series

The OM656 is based on a modular design shared with other 4-cylinder and 6-cylinder petrol and diesel engines. It replaces the previous V6 to maintain production cost efficiency across different engine types. The OM656 features dual overhead camshafts with variable valve timing and uses AdBlue injection and exhaust gas recirculation to reduce emissions. The cylinder walls are coated with arc-sprayed steel, whose increased porosity improves oil film strength and reduces friction.

Higher Performance, Lower Fuel Consumption and Emissions

The latest engine delivers noticeably more power than its predecessor while achieving up to 6% better fuel efficiency. Key features of this top-tier diesel engine include:

Advanced stepped-bowl combustion process

Two-stage turbocharging

Introduction of CAMTRONIC variable valve-lift control

Its construction combines an aluminium engine block with durable steel pistons and enhanced NANOSLIDE® cylinder wall coating for improved performance and reduced friction.

This new six-cylinder diesel engine is engineered to meet upcoming emissions standards, including RDE (Real Driving Emissions). All critical components for emissions control are integrated directly on the engine. By combining the stepped-bowl combustion design, dynamic multi-path exhaust gas recirculation, near-engine exhaust aftertreatment, and variable valve-lift technology, the engine achieves optimized fuel efficiency with reduced emissions. The near-engine insulated layout minimizes heat loss in the exhaust aftertreatment system, ensuring highly efficient operation under real-world driving conditions.

OM656.929 Engine Common Issues and Detailed Analysis

Emission System Issues — DPF Regeneration Failure / EGR Carbon Build-up

Common Symptoms:

1. MIL (Malfunction Indicator Lamp) illuminates
2. Power loss during driving
3. Frequent DPF regeneration failure warnings
4. Unstable idle and black exhaust smoke

Detailed Causes:

DPF (Diesel Particulate Filter) clogging

1. High dependence on DPF for emission control
2. Low-speed or short trips fail to reach regeneration temperature, accelerating carbon accumulation
3. Poor fuel quality or burning of engine oil accelerates soot build-up
4. Extended idling or city traffic prevents effective regeneration

EGR (Exhaust Gas Recirculation) valve carbon build-up

1. EGR recirculates high-temperature exhaust gas, which can cause carbon deposits over time
2. Carbon accumulation in the cooling paths or valve body may lead to sticking or malfunction

Repair Solutions:

1. Use professional diagnostic tools (e.g., XENTRY / DTS Monaco) to read fault codes
2. Force DPF regeneration, cleaning, or replacement
3. Remove and deeply clean or replace the EGR valve assembly
4. Check temperature and pressure sensors for false readings

Preventive Maintenance:

1. Regular high-speed driving (at least once per week)
2. Use high-quality low-sulfur diesel and OEM-approved engine oil
3. Inspect DPF condition every 20,000–30,000 km
4. Soft-clean EGR cooling passages and valve periodically

High-Pressure Fuel System Issues (Pump & Injector Failure)

Common Symptoms:

• Difficult starting or temporary stall after start
• Idle vibration and power loss
• Black smoke and abnormal fuel consumption

Detailed Causes:

• High-pressure common-rail system with pressures exceeding 2000 bar

High-pressure pump wear

• Gear and plunger wear reduces output pressure
• Internal leakage causes unstable fuel supply

Injector nozzle blockage or wear

• Diesel impurities or varnish block injector holes
• Solenoid aging affects timing and spray pattern

Repair Solutions:

• Test high-pressure pump pressure for stability
• Inspect injectors and replace faulty ones
• Replace high-pressure fuel line seals and filters

Preventive Maintenance:

• Regular diesel filter replacement (especially in city driving)
• Use certified fuel to avoid water or impurities
• Periodically clean injectors or use injector cleaning additives

Summary of OM656.929 Weak Points:

• Emission control system
• High-pressure fuel supply
• Turbo lubrication and cooling management

Most failures relate to:

• Fuel quality
• Driving conditions
• Maintenance intervals

Preventive strategy:

• Regular inspections, high-quality oils and fuels, and scientific maintenance practices

OM656.929 Engine Advantages

High Performance and Efficiency

• Strong power output: Smooth torque and higher than the previous V6 diesel
• Fuel efficiency: Up to 5–6% improvement over previous generation due to stepped-bowl combustion and twin-stage turbocharging
• Low friction design: NANOSLIDE® cylinder coating with steel pistons reduces wear

Advanced Emission Control

• Compliant with RDE standards, reducing NOx and particulate emissions
• Integrated EGR, near-engine exhaust aftertreatment, and AdBlue injection ensures low emissions without sacrificing performance

Modular and Lightweight Design

• Shared platform with other 4- and 6-cylinder petrol and diesel engines reduces production and maintenance costs
• Aluminium block + steel pistons improve power-to-weight ratio and fuel efficiency

Smoothness and Comfort

• Inline-six naturally balanced for low vibration and smooth operation
• CAMTRONIC variable valve-lift optimizes low and high RPM performance for improved driving comfort

OM656.929 Engine Applications

Driving Scenarios:

• Long-distance cruising and highway driving: Matched with DCT + turbo for efficient fuel economy
• City commuting and business vehicles: Smooth operation, low noise, minimal vibration
• Strict emission regions: Europe, Middle East, and other markets with stringent standards

Market Distribution:

• Europe: Germany, UK, France, Northern Europe – Diesel still dominant
• Middle East & Asia: Luxury SUVs and business vehicles
• North America: Limited diesel adoption, mainly high-end business cars and SUVs
• OM656.929 is among the most widely deployed engines in Europe, especially in luxury SUVs and high-end business sedans.

Yeahengine OM656.929 Engine Advantages

At Yeahengine, our OM656.929 engines are strictly manufactured according to original factory design specifications and match Mercedes-Benz OEM standards.

High-precision machining and advanced assembly ensure stable performance and durability.

Every engine undergoes multiple quality checks, including pressure testing, torque testing, and sealing inspection.

European customers frequently order this engine and consistently provide positive feedback, helping us gain many distributor clients.

All remanufactured engines use original OEM parts to ensure the quality of critical components. Every engine undergoes strict remanufacturing processes and full testing, from disassembly, cleaning, precision machining to assembly. Each step meets original factory standards, guaranteeing performance and durability equivalent to a new engine.

Our products match OEM quality while offering competitive pricing, making them ideal for customers needing engine repair, replacement, or upgrades.

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