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Mercedes-Benz M256 Engine - Replacement Cost, Problems & CompatibilityProblems & Compatibility
The M256 is Mercedes-Benz’s revolutionary 3.0-litre inline-6 turbocharged petrol engine, famous for its integrated 48V mild-hybrid system (EQ Boost) and electric auxiliary compressor. Fitted to the W213 E-Class, W222/W223 S-Class, W167 GLE, and AMG 53 models, reconditioned M256 engines typically start from £6,500 , serving as the definitive modern powerhouse for executive and performance Mercedes restorations.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
Used from
£3,500
Reconditioned from
£6,500
Rebuilt from
£9,500
GB
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Key Specs
Mercedes-Benz M256 - Specifications at a Glance
Engine Code
M256 (including M256.930, M256.940)
Fuel
Petrol
Configuration
3.0L inline-6, DOHC, 24-valve, twin-scroll turbo, 48V mild-hybrid (EQ Boost)
Power Output(s)
270 kW (367 hp) - 320 kW (435 hp)
Years Produced
2017-Present
UK Models Fitted
5 Mercedes model families - full list in Compatibility below
Replaced
M276 (3.0L V6 Biturbo)
Replaced By
Still in production (evolving into PHEV variants)
Most Common Failure
48V Integrated Starter Generator (ISG) failure and coolant leaks
Reconditioned Price Range
£6,500-£9,500 supply-only
Vetted UK specialists for M256 replacements
Minimum 12-month warranty on reconditioned and rebuilt options
Fitted To
Which Mercedes Models Use the M256.930/940-
The M256 marked a monumental shift for Mercedes-Benz, retiring the V6 architecture in favour of a smoother, more efficient, and highly modular inline-6 design. The integration of the 48V electrical system provides seamless start-stop functionality and a temporary 22 hp torque fill via the ISG.
| Model | Generation/Chassis | Badge(s) | Years | Link |
|---|---|---|---|---|
 Mercedes-Benz E-Class | W213 (Facelift) | E 450, AMG E 53 | 2018-2023 | |
| Mercedes-Benz S-Class | W222 (Facelift) / W223 | S 450, S 500, AMG S 53 / S 63 | 2017-Present | |
| Mercedes-Benz GLE-Class | W167 | GLE 450, AMG GLE 53 | 2019-Present | |
| Mercedes-Benz CLS-Class | C257 (Facelift) | CLS 450, AMG CLS 53 | 2018-2023 | |
| Mercedes-Benz AMG GT 4-Door | X290 | AMG GT 53 | 2019-Present |
02
Mercedes-Benz S-Class
Generation/Chassis
W222 (Facelift) / W223
Badge(s)
S 450, S 500, AMG S 53 / S 63
Years
2017-Present
Link
03
Mercedes-Benz GLE-Class
04
Mercedes-Benz CLS-Class
Generation/Chassis
C257 (Facelift)
Badge(s)
CLS 450, AMG CLS 53
Years
2018-2023
05
Mercedes-Benz AMG GT 4-Door
CROSS-BRAND
M256 is documented across 5 BMW applications spanning E-Class, S-Class, GLE-Class, CLS-Class, AMG GT 4-Door. Registration lookup confirms the exact suffix before quotes are sent.
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Not sure which engine your car has- Enter your registration above - we'll confirm your exact M256 fitment before any quotes are sent.
Prices
Mercedes-Benz M256 Engine Replacement Cost (UK)
Condition | Supply Only | Fitted (Independent Specialist) | Typical Warranty |
|---|---|---|---|
Used | £3,500-£5,500 | £4,500-£7,000 | 3-6 months |
Reconditioned | £6,500-£9,500 | £8,000-£11,500 | 12-24 months |
Rebuilt | £9,500-£14,000 | £11,500-£16,500 | 12-24 months |
What genuinely moves the price for this engine is the health of the 48V Integrated Starter Generator (ISG), the electric auxiliary compressor (on AMG 53 models), and the plastic coolant housing assemblies. Because the M256 is a highly complex modern unit, reputable recon specialists will typically test the ISG, replace all brittle plastic coolant components with updated revisions, and perform a full software calibration as standard. For a full breakdown of market rates, see our full reconditioned engine cost guide.
Labour Guide
Fitting an M256 engine typically takes 14-20 hours at £85-£110/hr (AMG/modern Mercedes specialist) - the tight packaging of the 48V components and ancillary drives makes extraction labour-intensive.
Price Factors
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Common Problems
Mercedes-Benz M256 Engine Problems - What Actually Fails
Every engine has its weak points. Here are the known issues with the M256, based on real-world data and verified failure patterns.
Verified issue focus: 48V Integrated Starter Generator (ISG) failure and coolant leaks.
1. 48V Integrated Starter Generator (ISG) Failure
1. 48V Integrated Starter Generator (ISG) Failure
Typical onset:
40,000-80,000 miles (predominantly 2017-2019 models)
What happens:
The ISG, which replaces the traditional alternator and starter motor, is prone to internal electrical faults or bearing wear. This triggers a "48V Electrical System Fault" warning, leading to a no-start condition, limp mode, or the engine failing to restart after an auto-stop.
Repair vs replace:
Early ISG units were subject to manufacturer recalls and software updates. If the hardware has failed, the entire ISG unit must be replaced, which is a costly but straightforward bolt-on procedure.
Read more about this issue
2. Coolant Leaks (Electric Water Pump & Thermostat Housing)
2. Coolant Leaks (Electric Water Pump & Thermostat Housing)
Typical onset:
50,000-90,000 miles
What happens:
The M256 utilizes several plastic coolant housing components and an electric auxiliary water pump. Over time, the constant heat cycles cause these plastic components to warp or crack, leading to external coolant leaks or internal mixing.
Repair vs replace:
Mercedes has released updated, more durable revisions of these components. Replacing the faulty housing and pump is a standard repair, but ignoring it can lead to overheating and severe engine damage.
Read more about this issue
3. Timing Chain Stretch and Guide Wear
3. Timing Chain Stretch and Guide Wear
Typical onset:
70,000+ miles (early production models)
What happens:
While generally robust, some early M256 engines exhibited premature timing chain stretch or guide wear, manifesting as a faint rattling noise on cold starts or camshaft position correlation fault codes.
Repair vs replace:
If caught early, replacing the timing chain kit and updated guides is a known, albeit labour-intensive, repair. If ignored, it can lead to timing jumps and catastrophic valve-to-piston contact.
Read more about this issue
Post-2020 M256 engines feature revised ISG hardware, updated coolant component materials, and improved timing chain tensioners, making them significantly more robust and reliable than the initial launch models .
Compare rebuilt M256 engine prices with the failure already addressed
Engine Variants
M256 Sub-Codes Explained - Which One Is in Your Car-
INTRO: The M256 family shares the same fundamental 3.0L DOHC inline-6 block architecture and 48V mild-hybrid foundation, but turbocharging strategy, auxiliary compression, and ECU mapping vary significantly between standard and AMG applications. Identifying your exact sub-code is mandatory. - Fitted to: E-Class W213 (E 450), S-Class W222/W223 (S 450, S 500), GLE-Class W167 (GLE 450) - Key technical difference: The standard-output variant, relying on a single twin-scroll turbocharger and the 48V ISG for smooth power delivery and efficiency. It lacks the electric auxiliary compressor found in AMG models. - Sub-code-specific failure note: Shares the family failure pattern above; ISG and coolant housing leaks are the primary wear items. - Interchange note: Not a straight swap with AMG variants due to different ECU mapping, exhaust plumbing, and the absence of the electric auxiliary compressor (EAC) hardware. - Fitted to: E-Class W213 (AMG E 53), S-Class W222 (AMG S 53), AMG GT 4-Door X290 (AMG GT 53) - Key technical difference: The high-performance AMG variant. In addition to the twin-scroll turbo and ISG, it features an Electric Auxiliary Compressor (EAC) mounted at the front of the engine to eliminate turbo lag entirely, alongside a more aggressive camshaft profile and AMG-specific engine management. - Sub-code-specific failure note: Shares the family failure pattern above; the EAC adds another potential point of electrical or mechanical failure, and the higher thermal loads can accelerate coolant component degradation. - Interchange note: Requires matching EAC hardware, specific AMG wiring harnesses, and dedicated AMG ECU calibration; not interchangeable with standard .930 variants.
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. Not sure- Enter your registration above for instant confirmation.
Easily Confused
M276
the 3.0L V6 biturbo that the M256 replaced across the E-Class, S-Class, and GLE range, offering a shift to a smoother, more efficient inline-6 architecture with integrated 48V mild-hybrid technology.
Alternative / Next-Gen Code
M254
the 2.0L inline-4 48V mild-hybrid engine that shares the same modular design philosophy and EQ Boost integration as the M256, but with lower displacement and output for core compact and mid-size applications.
Related JLR Variants
M177
the 4.0L V8 biturbo that sits above the M256 in the AMG hierarchy, sharing the modern "Hot-Vee" turbo layout philosophy but delivering significantly higher power for flagship performance models.
Confirm the exact M256 fitment
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. Not sure- Enter your registration above for instant confirmation.
Buying Guide
Buying a Replacement M256 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:
Buying a used M256 engine carries significant financial risk unless it comes with a full, stamped service history and documented proof that the ISG and coolant components have been inspected or replaced under warranty. Given the high cost of modern Mercedes electronics, purchasing a used unit with unknown history is highly discouraged.
Reconditioned:
A proper reconditioned M256 engine is the sweet spot for most buyers. A reputable rebuild will proactively address the common failure points by testing or replacing the ISG, upgrading all plastic coolant components to the latest revised parts, and ensuring the timing chain assembly is within strict factory tolerances.
Rebuilt:
A full M156/M256 engine rebuild is highly justified for high-mileage AMG 53 models or S-Class hosts where maximum longevity, track capability, or originality is required. An upgraded rebuild should include precision balancing and the installation of the absolute latest factory-revised components.
Supply & Fit Line:
Sourcing and fitting through our vetted network ensures your M256 engine is installed by specialists equipped with the latest Mercedes diagnostic software to calibrate the 48V system, backed by a nationwide warranty.
Vehicle Value Note:
Because the M256 is found in modern executive and AMG vehicles valued between £25,000 and £80,000+, a full engine replacement is a financially viable necessity to protect the asset's value. However, due to the high cost of the engine and specialized labour, always ensure the replacement cost is weighed against the vehicle's current market valuation .
Compare M256 Engine Prices Now
Related Engines
Engines Related to the Mercedes-Benz M256
Explore engines that are closely related to the Mercedes-Benz M256, including its predecessor, successor, and key family variants.
Predecessor
M276
the 3.0L V6 biturbo that the M256 replaced across the E-Class, S-Class, and GLE range, offering a shift to a smoother, more efficient inline-6 architecture with integrated 48V mild-hybrid technology.
Sibling
M254
the 2.0L inline-4 48V mild-hybrid engine that shares the same modular design philosophy and EQ Boost integration as the M256, but with lower displacement and output for core compact and mid-size applications.
Sibling
M177
the 4.0L V8 biturbo that sits above the M256 in the AMG hierarchy, sharing the modern "Hot-Vee" turbo layout philosophy but delivering significantly higher power for flagship performance models.
FAQ
Mercedes-Benz M256Frequently Asked Questions
Question 1How much does a Mercedes M256 engine replacement cost-
A reconditioned Mercedes M256 engine typically costs between £6,500 and £9,500 for supply only . Fitted costs generally range from £8,000 to £11,500 depending on the specialist, while used units can be found from £3,500 but carry a high financial risk due to the potential for 48V ISG and coolant component failures. Compare M256 engine replacement quotes today
Compare M256 quotesQuestion 2What is the most common failure on the M256 engine-
The most documented issues are 48V Integrated Starter Generator (ISG) failure, plastic coolant housing and electric water pump leaks, and early timing chain stretch. The ISG can trigger no-start conditions or limp mode, while degraded plastic coolant components can lead to overheating if not addressed promptly. Get quotes for a rebuilt M256 with these issues resolved
Compare M256 quotesQuestion 3Which Mercedes models use the M256 engine-
The M256.930 and .940 variants were fitted to the W213 E-Class (E 450, AMG E 53), the W222/W223 S-Class (S 450, S 500, AMG S 53), the W167 GLE-Class (GLE 450, AMG GLE 53), the C257 CLS-Class (CLS 450, AMG CLS 53), and the X290 AMG GT 4-Door (AMG GT 53), serving as the definitive modern inline-6 for these chassis from 2017 onwards. Check your registration to confirm your exact M256 fitment
Compare M256 quotesQuestion 4Should I buy a used or reconditioned M256 engine-
A reconditioned M256 is strongly recommended over a used unit. A proper rebuild will proactively address the common failure points by testing or replacing the 48V ISG, upgrading all plastic coolant components to the latest revised factory parts, and verifying the timing chain assembly, whereas a used engine with unknown history risks immediate, costly electrical or cooling system repairs. Compare reconditioned M256 engine prices from UK specialists
Compare M256 quotesQuestion 5What is the difference between M256.930 and M256.940-
The M256.930 is the standard-output variant (found in E 450, S 450/500) relying on a single twin-scroll turbo and the 48V ISG. The M256.940 is the high-performance AMG variant (found in AMG 53 models) which adds an Electric Auxiliary Compressor (EAC) to eliminate turbo lag, alongside a more aggressive camshaft profile and AMG-specific engine management. They share the same core block, but the EAC hardware, wiring, and ECU mapping differ significantly. Enter your reg above to identify your exact M256 sub-code ═══════════════════════════════════════
Compare M256 quotesCompare Mercedes-Benz M256 Engine Prices Today
Vetted UK specialists who work on modern Mercedes 48V mild-hybrid systems like the M256 every week Minimum 12-month warranty on every reconditioned and rebuilt M256 engine Nationwide delivery - supply-only or full supply & fit available across the UK Get a free, no-obligation comparison of M256 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 a verified 48V ISG, updated coolant components, and precise factory tolerances. With reconditioned M256 engines starting from an estimated £6,500, comparing takes two minutes and could save you thousands on labour and unexpected teardowns.
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Vetted UK specialists for M256 replacements
Minimum 12-Month Warranty
Minimum 12-month warranty on reconditioned and rebuilt options
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