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Mercedes-Benz OM656 Engine - Replacement Cost, Problems & CompatibilityProblems & Compatibility
The OM656 is Mercedes-Benz’s modern 3.0-litre inline-6 common-rail diesel (CDI), featuring 48V mild-hybrid (EQ Boost) integration and fitted to the W213 E-Class, W222/W223 S-Class, and W167 GLE. Reconditioned OM656 engines typically start from £3,200 , serving as the definitive premium diesel for modern flagship and executive chassis.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
Used from
£1,800
Reconditioned from
£3,200
Rebuilt from
£4,500
GB
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Quotes only from vetted UK engine specialists.
Key Specs
Mercedes-Benz OM656 - Specifications at a Glance
Engine Code
OM656 (including OM656.930, OM656.940)
Fuel
Diesel
Configuration
3.0L inline-6, DOHC, 24-valve, common-rail (CDI) with 48V mild-hybrid (EQ Boost)
Power Output(s)
183 kW (249 hp) - 243 kW (330 hp)
Years Produced
2018-Present
UK Models Fitted
4 Mercedes model families - full list in Compatibility below
Replaced
OM642
Replaced By
Still in production
Most Common Failure
AdBlue system faults and EGR cooler leaks
Reconditioned Price Range
£3,200-£5,500 supply-only
Vetted UK specialists for OM656 replacements
Minimum 12-month warranty on reconditioned and rebuilt options
Fitted To
Which Mercedes Models Use the OM656-
The OM656 is the definitive modern 6-cylinder diesel for Mercedes-Benz, replacing the older V6 OM642 with a smoother, more efficient inline-6 architecture that integrates seamlessly with the brand's 48V mild-hybrid electrical systems.
| Model | Generation/Chassis | Badge(s) | Years | Link |
|---|---|---|---|---|
 Mercedes-Benz E-Class | W213 (Facelift) | E 300 d, E 400 d | 2018-2023 | |
| Mercedes-Benz S-Class | W222 (Facelift) / W223 | S 350 d, S 400 d | 2018-Present | |
| Mercedes-Benz GLE-Class | W167 | GLE 300 d, GLE 400 d | 2019-Present | |
| Mercedes-Benz GLS-Class | X167 | GLS 400 d | 2019-Present |
02
Mercedes-Benz S-Class
03
Mercedes-Benz GLE-Class
04
Mercedes-Benz GLS-Class
CROSS-BRAND
OM656 is documented across 4 BMW applications spanning E-Class, S-Class, GLE-Class, GLS-Class. Registration lookup confirms the exact suffix before quotes are sent.
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Prices
Mercedes-Benz OM656 Engine Replacement Cost (UK)
Condition | Supply Only | Fitted (Independent Specialist) | Typical Warranty |
|---|---|---|---|
Used | £1,800-£3,200 | £2,450-£4,110 | 3-6 months |
Reconditioned | £3,200-£5,500 | £3,850-£6,410 | 12-24 months |
Rebuilt | £4,500-£7,000 | £5,150-£7,910 | 12-24 months |
What genuinely moves the price for this engine is the condition of the AdBlue dosing module, the EGR cooler, and the 48V Integrated Starter Generator (ISG). Because the OM656 is a highly complex modern common-rail unit, recon specialists will typically verify the ISG health, update all software maps, and replace the EGR cooler as standard. For a full breakdown of market rates, see our full reconditioned engine cost guide.
Labour Guide
Fitting an OM656 engine typically takes 10-14 hours at £65-£85/hr (independent) - confirm exact labour when comparing quotes.
Price Factors
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Common Problems
Mercedes-Benz OM656 Engine Problems - What Actually Fails
Every engine has its weak points. Here are the known issues with the OM656, based on real-world data and verified failure patterns.
Verified issue focus: AdBlue system faults and EGR cooler leaks.
1. AdBlue System Faults
1. AdBlue System Faults
Typical onset:
80,000-150,000 miles
What happens:
The AdBlue dosing module, heater, or NOx sensors can fail, leading to warning lights, restricted performance (limp mode), and eventually a no-start condition if the tank is depleted and the system is locked out by the ECU.
Repair vs replace:
Often resolved by replacing the dosing module or NOx sensor, which is a standard repair. If the tank heater or pump has failed, a full tank assembly replacement may be required.
Read more about this issue
2. EGR Cooler Leaks
2. EGR Cooler Leaks
Typical onset:
80,000-150,000 miles
What happens:
The internal matrix of the EGR cooler can crack, allowing coolant to mix with exhaust gases or enter the intake manifold. This leads to unexplained coolant loss, white smoke from the exhaust, and potential hydrolock if severe.
Repair vs replace:
EGR cooler replacement is a standard repair. If caught early, it prevents catastrophic internal engine damage.
Read more about this issue
3. Mild-Hybrid (ISG) Integration Issues
3. Mild-Hybrid (ISG) Integration Issues
Typical onset:
60,000+ miles
What happens:
The Integrated Starter Generator (ISG) is a complex 48V component. While generally reliable, software glitches or electrical faults can cause start-stop malfunctions, reduced EQ Boost assistance, or warning lights.
Repair vs replace:
Most ISG issues are resolved via software updates or replacing the 48V auxiliary battery. Full ISG replacement is rare but costly if the unit itself fails.
Read more about this issue
The OM656 is generally considered a highly robust and reliable modern diesel, representing a significant refinement and durability step up from the older V6 OM642 it replaced. Units maintained with strict AdBlue top-ups and regular oil changes routinely exceed 150,000 miles without major internal issues .
Compare rebuilt OM656 engine prices with the failure already addressed
Engine Variants
How to Confirm You Have the Mercedes-Benz OM656
The engine code is stamped on the right-hand side of the cylinder block, near the oil filter housing. It will also be listed on your V5C logbook under "Engine Capacity" or visible via a VIN decode. The OM656 is sometimes confused with the older 3.0L V6 OM642 or the smaller 2.0L inline-4 OM654. Fitting the wrong revision or assuming interchangeability matters significantly: the OM656 features a specific modular inline-6 design, distinct 48V mild-hybrid wiring looms, and specific ECU mapping that will not function correctly if swapped with an OM642 or OM654 without extensive and costly modification.
Not sure which engine your car has- Enter your registration above - we'll confirm your exact OM656 fitment before any quotes are sent.
Easily Confused
OM642
the 3.0L V6 CDI that the OM656 replaced, offering a shift to a smoother, more efficient inline-6 architecture with integrated 48V mild-hybrid technology.
Alternative / Next-Gen Code
OM656.950
the updated variant of the OM656 family, featuring further refined emissions hardware and mild-hybrid integration for the latest chassis applications.
Related JLR Variants
OM654
the 2.0L inline-4 CDI that sits directly below the OM656 in the hierarchy, sharing the same modular design philosophy and 48V mild-hybrid integration but with lower output for core saloon applications.
Confirm the exact OM656 fitment
Not sure which engine your car has- Enter your registration above - we'll confirm your exact OM656 fitment before any quotes are sent.
Buying Guide
Buying a Replacement OM656 Engine - What to Choose
Choosing the right replacement route depends on your budget, risk tolerance, and ownership goals. Here's a breakdown of your options.
Used:
A used OM656 engine makes sense only if it comes with verifiable service history and documented proof that the AdBlue system, EGR cooler, and 48V ISG are in good working order. Given the complexity of modern hybrid emissions systems, buying a used unit with unknown history is a significant financial risk.
Reconditioned:
A proper reconditioned OM656 engine is the sweet spot for most buyers. A reputable rebuild will proactively address the common failure points by verifying the AdBlue dosing module, replacing the EGR cooler, and refreshing all critical seals, giving the engine a fresh lease on life.
Rebuilt:
A full OM656 engine rebuild is justified for high-mileage W223 S-Class or W167 GLE hosts where maximum longevity and originality are required. An upgraded rebuild should include line-boring the block, new pistons/rings, and a balanced crankshaft.
Supply & Fit Line:
Sourcing and fitting through our vetted network ensures your OM656 engine is installed by specialists familiar with modern Mercedes CDI and mild-hybrid systems, backed by a nationwide warranty.
Vehicle Value Note:
Because the OM656 is typically found in modern W213, W222/W223, and W167 vehicles valued between £15,000 and £60,000+, a full replacement is highly financially viable and comfortably within the host vehicle's value . Replacement cost rarely exceeds the scrap threshold for these modern chassis, making a reconditioned unit a highly sensible investment.
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Related Engines
Engines Related to the Mercedes-Benz OM656
Explore engines that are closely related to the Mercedes-Benz OM656, including its predecessor, successor, and key family variants.
Predecessor
OM642
the 3.0L V6 CDI that the OM656 replaced, offering a shift to a smoother, more efficient inline-6 architecture with integrated 48V mild-hybrid technology.
Successor
OM656.950
the updated variant of the OM656 family, featuring further refined emissions hardware and mild-hybrid integration for the latest chassis applications.
Sibling
OM654
the 2.0L inline-4 CDI that sits directly below the OM656 in the hierarchy, sharing the same modular design philosophy and 48V mild-hybrid integration but with lower output for core saloon applications.
FAQ
Mercedes-Benz OM656Frequently Asked Questions
Question 1How much does a Mercedes OM656 engine replacement cost-
A reconditioned Mercedes OM656 engine typically costs between £3,200 and £5,500 for supply only . Fitted costs generally range from £3,850 to £6,410 depending on the specialist, while used units can be found from £1,800 but carry higher risk due to the complexity of the modern emissions and hybrid systems. Compare OM656 engine replacement quotes today
Compare OM656 quotesQuestion 2What is the most common failure on the OM656 engine-
The most documented issues are AdBlue system faults, EGR cooler leaks, and occasional mild-hybrid (ISG) integration issues. AdBlue dosing module or NOx sensor failures trigger limp mode, while EGR cooler cracks can lead to unexplained coolant loss and white smoke from the exhaust. Get quotes for a rebuilt OM656 with these issues resolved
Compare OM656 quotesQuestion 3Which Mercedes models use the OM656 engine-
The OM656.930 and .940 were fitted to the W213 E-Class facelift (E 300 d, E 400 d), the W222/W223 S-Class (S 350 d, S 400 d), the W167 GLE-Class (GLE 300 d, GLE 400 d), and the X167 GLS-Class (GLS 400 d), serving as the definitive modern 6-cylinder diesel for these premium chassis from 2018 onwards. Check your registration to confirm your exact OM656 fitment
Compare OM656 quotesQuestion 4Should I buy a used or reconditioned OM656 engine-
A reconditioned OM656 is strongly recommended over a used unit. A proper rebuild will proactively address the common failure points by verifying the AdBlue dosing module, replacing the EGR cooler, and refreshing all critical seals, whereas a used engine with unknown history risks hidden emissions system faults. Compare reconditioned OM656 engine prices from UK specialists
Compare OM656 quotesQuestion 5How do I know if my car has the OM656 and not the OM642 or OM654-
The OM656 is a distinct 3.0L inline-6 common-rail diesel with 48V mild-hybrid integration, producing a unique sound and performance profile compared to the older 3.0L V6 OM642 or the smaller 2.0L inline-4 OM654. The engine code is stamped on the right-hand side of the cylinder block near the oil filter housing and is also listed on your V5C logbook. Enter your reg above to identify your exact engine code ═══════════════════════════════════════
Compare OM656 quotesCompare Mercedes-Benz OM656 Engine Prices Today
Vetted UK specialists who work on modern Mercedes CDI and mild-hybrid systems like the OM656 every week Minimum 12-month warranty on every reconditioned and rebuilt OM656 engine Nationwide delivery - supply-only or full supply & fit available across the UK Get a free, no-obligation comparison of OM656 engine prices tailored to your exact vehicle. Our registration lookup confirms your fitment before any quotes are sent, ensuring you receive the correct unit with verified AdBlue, EGR, and 48V ISG components. With reconditioned OM656 engines starting from an estimated £3,200, comparing takes two minutes and could save you hundreds on labour and unexpected teardowns.
Vetted UK Specialists
Vetted UK specialists for OM656 replacements
Minimum 12-Month Warranty
Minimum 12-month warranty on reconditioned and rebuilt options
Nationwide Delivery
Nationwide delivery plus supply and fit availability
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