How much does a Mercedes C257 engine replacement cost in the UK?

A reconditioned C257 engine typically costs £2,500–£8,500 supply only, depending on the engine — the OM654 diesel sits at £2,800–£4,800, while the M256 petrol is £3,500–£6,500 and the AMG M256 is £4,500–£8,500. Fitting adds £650–£1,500 depending on the variant. Use our calculator for a personalised quote.

Which C257 engine is the most reliable?

The OM654 2.0-litre diesel (CLS 220 d) is the most reliable choice — it's Mercedes-developed, efficient, and has a strong track record when serviced properly. The M256 3.0-litre inline-six petrol is also very refined and dependable, though its EQ Boost system adds complexity.

What are the common problems with the C257?

The OM654 diesel can suffer from injector seal leaks (known as 'Black Death'); the M256 petrol engine can develop coolant leaks and EQ Boost system issues; and the OM656 inline-six diesel can experience AdBlue/SCR system failures. Regular servicing is key.

Is the Mercedes C257 reliable overall?

Yes — the C257 is generally well-regarded for reliability, especially with the OM654 diesel and M264/M256 petrol engines. The OM656 inline-six diesel is also reliable but more complex due to its twin-turbo and AdBlue systems. All engines benefit from regular, attentive servicing.

Which C257 engine should I avoid?

No engine outright — but the OM656 high-output diesel (CLS 400 d) was a short-production variant (2018–2019) and parts may be harder to source. The AMG CLS 53 is not an engine to avoid, but buyers should be aware of the higher running costs. Any C257 without documented service history should be approached with caution.

How do I know if my C257 engine needs replacing?

Warning signs include a ticking noise from the engine bay (OM654 injector seals), coolant loss (M256 water pump), AdBlue warnings (OM656 SCR system), or EQ Boost system errors (M256). If you notice any of these, have the car inspected immediately — ignoring them can lead to a full engine failure.

How long do Mercedes C257 engines last?

The OM654 diesel can easily exceed 150,000 miles with regular servicing and early attention to the injector seals. The M256 inline-six petrol is similarly durable, though its EQ Boost system may require attention at higher mileages. The OM656 inline-six diesel can also reach high mileages with proper care.

What is the difference between the C257 and the previous C218?

The C257 is the third-generation CLS, built on the newer MRA platform (shared with the E-Class W213). It introduced a new range of electrified engines (M264, M256, OM654, OM656) with EQ Boost mild-hybrid technology, improved interior quality, and updated technology. The C218 (2010–2018) used older M276 and OM642 engines and is covered on its own generation page.

How do I find my Mercedes C257 engine code?

The engine code is on the VIN plate (visible through the windscreen), on the vehicle documentation, and stamped on the engine block. For the C257, common codes are M264 (petrol, 2.0L), M256 (petrol, 3.0L), OM654 (diesel, 2.0L), and OM656 (diesel, 2.9L). Tell us your variant and year, and we'll identify it — 25+ vetted Mercedes specialists will confirm it for free.

C257 Engine Replacement Cost UK

Name: Mercedes CLS C257 UK Engine Enquiry Data 2025
Creator: MercedesEngines.uk

Mercedes CLS C257 Engine Codes — The Complete Database

Every engine fitted to the C257 specifically — including the M264 four-cylinder petrol, the M256 inline-six petrol, and the OM654/OM656 diesel range.

Engine CodeFamilyFuelDisplacementPowerYears (C257)Variants (badges)Reliability2025 EnquiriesAvg. Recon Cost

M264.920M264Petrol, turbo + EQ Boost2.0L (1991cc)295–299 bhp2018–2021CLS 350, CLS 350 4MATIC★★★★☆ [PROVISIONAL — well-regarded M264 four-cylinder]390 [MB-VERIFIED]£2,500–£5,000 [MB-QUOTE]

M256.930M256Petrol, turbo + EQ Boost3.0L (2999cc)362–367 bhp2018–2023CLS 450 4MATIC, CLS 450 4MATIC+★★★★½ [PROVISIONAL — Mercedes inline-six; refined and reliable]— (pattern data)£3,500–£6,500 [MB-QUOTE]

M256.930 (AMG)M256Petrol, twin-turbo + EQ Boost3.0L (2999cc)429–435 bhp2018–2023AMG CLS 53 4MATIC+★★★★☆ [PROVISIONAL — AMG-tuned M256; powerful but demanding]370 [MB-VERIFIED]£4,500–£8,500 [MB-QUOTE]

OM654.920OM654Diesel, turbo2.0L (1950cc)191–194 bhp2018–2023CLS 220 d★★★★☆ [PROVISIONAL — Mercedes-developed four-cylinder diesel]520 [MB-VERIFIED]£2,800–£4,800 [MB-QUOTE]

OM654.920 (high-output)OM654 MDiesel, turbo + EQ Boost2.0L (1993cc)261–265 bhp2021–2023 (facelift)CLS 300 d 4MATIC★★★★☆ [PROVISIONAL — updated OM654 with mild hybrid]520 [MB-VERIFIED]£3,000–£5,200 [MB-QUOTE]

OM656.929OM656Diesel, twin-turbo2.9L (2925cc)249 bhp2018–2022CLS 350 d 4MATIC★★★★☆ [PROVISIONAL — Mercedes inline-six diesel]— (pattern data)£3,200–£5,500 [MB-QUOTE]

OM656.929 (high-output)OM656Diesel, twin-turbo2.9L (2925cc)340 bhp2018–2019 (early)CLS 400 d 4MATIC★★★★☆ [PROVISIONAL — high-output OM656; short production run]— (pattern data)£3,500–£6,000 [MB-QUOTE]

Engine CodeFuelPowerYearsReliabilityEnquiriesAvg. Recon Cost

M264.920M264Petrol, turbo + EQ Boost295–299 bhp2018–2021★★★★☆ [PROVISIONAL — well-regarded M264 four-cylinder]390 [MB-VERIFIED]£2,500–£5,000 [MB-QUOTE]

M256.930M256Petrol, turbo + EQ Boost362–367 bhp2018–2023★★★★½ [PROVISIONAL — Mercedes inline-six; refined and reliable]— (pattern data)£3,500–£6,500 [MB-QUOTE]

M256.930 (AMG)M256Petrol, twin-turbo + EQ Boost429–435 bhp2018–2023★★★★☆ [PROVISIONAL — AMG-tuned M256; powerful but demanding]370 [MB-VERIFIED]£4,500–£8,500 [MB-QUOTE]

OM654.920OM654Diesel, turbo191–194 bhp2018–2023★★★★☆ [PROVISIONAL — Mercedes-developed four-cylinder diesel]520 [MB-VERIFIED]£2,800–£4,800 [MB-QUOTE]

OM654.920 (high-output)OM654 MDiesel, turbo + EQ Boost261–265 bhp2021–2023 (facelift)★★★★☆ [PROVISIONAL — updated OM654 with mild hybrid]520 [MB-VERIFIED]£3,000–£5,200 [MB-QUOTE]

OM656.929OM656Diesel, twin-turbo249 bhp2018–2022★★★★☆ [PROVISIONAL — Mercedes inline-six diesel]— (pattern data)£3,200–£5,500 [MB-QUOTE]

OM656.929 (high-output)OM656Diesel, twin-turbo340 bhp2018–2019 (early)★★★★☆ [PROVISIONAL — high-output OM656; short production run]— (pattern data)£3,500–£6,000 [MB-QUOTE]

Overview

Mercedes CLS C257 — Overview

The C257 is the third generation of the Mercedes‑Benz CLS, a four‑door coupé launched in 2018 as the successor to the C218.

Built on the Mercedes MRA platform shared with the E‑Class (W213), it introduced a new range of electrified engines — from the 2.0‑litre M264 four‑cylinder petrol to the 3.0‑litre M256 inline‑six petrol and the OM656 inline‑six diesel, all featuring EQ Boost mild‑hybrid technology (48V) for improved efficiency and response. A facelift arrived in 2021, bringing a new OM654 M mild‑hybrid diesel for the CLS 300 d. Production ended in August 2023.

Key Facts

Platform

Mercedes MRA (shared with E‑Class W213, S‑Class W222)

Predecessor

C218 (2010–2018)

Successor

none (CLS discontinued after C257)

Sibling body styles in this generation

none (CLS is a standalone four‑door coupé)

Market Intelligence

The C257 CLS generated 520+ real UK engine enquiries in 2025 [MB‑VERIFIED], concentrated on the OM654 diesel as the most‑requested powertrain.

Mercedes CLS C257 — Overview

The C257 is the third generation of the Mercedes‑Benz CLS, a four‑door coupé launched in 2018 as the successor to the C218.

Built on the Mercedes MRA platform shared with the E‑Class (W213), it introduced a new range of electrified engines — from the 2.0‑litre M264 four‑cylinder petrol to the 3.0‑litre M256 inline‑six petrol and the OM656 inline‑six diesel, all featuring EQ Boost mild‑hybrid technology (48V) for improved efficiency and response. A facelift arrived in 2021, bringing a new OM654 M mild‑hybrid diesel for the CLS 300 d. Production ended in August 2023.

Key Facts

Platform

Mercedes MRA (shared with E‑Class W213, S‑Class W222)

Predecessor

C218 (2010–2018)

Successor

none (CLS discontinued after C257)

Sibling body styles in this generation

none (CLS is a standalone four‑door coupé)

Market Intelligence

The C257 CLS generated 520+ real UK engine enquiries in 2025 [MB‑VERIFIED], concentrated on the OM654 diesel as the most‑requested powertrain.

Best & Worst Engines

Best Diesel Overall

OM654.920 (CLS 220 d)

“Mercedes' own 2.0‑litre four‑cylinder diesel, introduced in 2016, is the pick of the C257 diesel range — efficient, refined, and backed by a strong reliability record when serviced properly.”

Who it's for: buyers who want a modern, efficient diesel for high‑mileage cruising.

Best Petrol Overall

M256.930 (CLS 450)

“Mercedes' 3.0‑litre inline‑six petrol, with 362 bhp and EQ Boost mild‑hybrid assistance, delivers effortless power and silky refinement. It's the defining engine of the C257 generation.”

Who it's for: buyers who want the full luxury coupé experience.

Highest Risk

OM656.929 (CLS 350 d / 400 d)

“The inline‑six diesel is generally reliable but complex; its twin‑turbo system and AdBlue/SCR components can be costly to repair if neglected. The CLS 400 d was a short‑production variant, making parts potentially harder to source.”

Who it's for: buyers who want six‑cylinder diesel refinement but can afford the premium maintenance.

Most Expensive Failure

M256.930 (CLS 450 / AMG CLS 53) — EQ Boost system and turbo

“The 48V mild‑hybrid system and turbocharger on the M256 can be costly to repair if issues arise. The AMG CLS 53's higher output adds further complexity.”

Who it's for: buyers who want AMG performance and can afford the premium running costs.

Best Value

OM654.920 (CLS 220 d)

“The entry‑level diesel offers the best balance of performance (194 bhp), economy (up to 51 mpg), and reliability. It's the sweet spot in the C257 range.”

Who it's for: fleet buyers and high‑mileage drivers.

Most Overlooked

M264.920 (CLS 350)

“The 2.0‑litre four‑cylinder petrol with EQ Boost delivers 299 bhp and genuine performance (0‑62 mph in 6.0 seconds). It's often overlooked in favour of the six‑cylinder but offers a compelling blend of performance and efficiency.”

Who it's for: buyers who want petrol power without the six‑cylinder running costs.

Best Diesel Overall

OM654.920 (CLS 220 d)

“Mercedes' own 2.0‑litre four‑cylinder diesel, introduced in 2016, is the pick of the C257 diesel range — efficient, refined, and backed by a strong reliability record when serviced properly.”

Who it's for: buyers who want a modern, efficient diesel for high‑mileage cruising.

Best Petrol Overall

M256.930 (CLS 450)

“Mercedes' 3.0‑litre inline‑six petrol, with 362 bhp and EQ Boost mild‑hybrid assistance, delivers effortless power and silky refinement. It's the defining engine of the C257 generation.”

Who it's for: buyers who want the full luxury coupé experience.

Highest Risk

OM656.929 (CLS 350 d / 400 d)

“The inline‑six diesel is generally reliable but complex; its twin‑turbo system and AdBlue/SCR components can be costly to repair if neglected. The CLS 400 d was a short‑production variant, making parts potentially harder to source.”

Who it's for: buyers who want six‑cylinder diesel refinement but can afford the premium maintenance.

Most Expensive Failure

M256.930 (CLS 450 / AMG CLS 53) — EQ Boost system and turbo

“The 48V mild‑hybrid system and turbocharger on the M256 can be costly to repair if issues arise. The AMG CLS 53's higher output adds further complexity.”

Who it's for: buyers who want AMG performance and can afford the premium running costs.

Best Value

OM654.920 (CLS 220 d)

“The entry‑level diesel offers the best balance of performance (194 bhp), economy (up to 51 mpg), and reliability. It's the sweet spot in the C257 range.”

Who it's for: fleet buyers and high‑mileage drivers.

Most Overlooked

M264.920 (CLS 350)

“The 2.0‑litre four‑cylinder petrol with EQ Boost delivers 299 bhp and genuine performance (0‑62 mph in 6.0 seconds). It's often overlooked in favour of the six‑cylinder but offers a compelling blend of performance and efficiency.”

Who it's for: buyers who want petrol power without the six‑cylinder running costs.

Mercedes CLS C257 — Ownership Economics

EngineTypical MileageCommon Major FailureRepair Cost (Specialist)Replacement Cost (Recon)Ownership Verdict

M264.920 (CLS 350)40k–80kTiming chain wear, carbon buildup£500–£1,200£2,500–£5,000

Good Value — refined four‑cylinder petrol.

M256.930 (CLS 450)50k–90kEQ Boost system, turbo wear, coolant leaks£800–£2,000£3,500–£6,500

Best Petrol — silky inline‑six, premium costs.

M256.930 (AMG CLS 53)30k–60kTurbo wear, cooling system, EQ Boost£1,000–£2,500£4,500–£8,500

AMG Tax — high performance, high running costs.

OM654.920 (CLS 220 d)80k–150kInjector seal leaks, DPF clogging£400–£1,200£2,800–£4,800

Best Diesel — efficient, durable, Mercedes‑developed.

OM654 M (CLS 300 d)60k–100kAdBlue system, EGR cooler£500–£1,500£3,000–£5,200

Modern Diesel — facelift tech, reliable.

OM656.929 (CLS 350 d / 400 d)60k–120kAdBlue/SCR issues, twin‑turbo wear£800–£2,000£3,200–£6,000

Six‑Cylinder Diesel — refined but complex.

EngineTypical MileageCommon Major FailureRepair Cost (Specialist)Replacement Cost (Recon)Ownership Verdict

M264.920 (CLS 350)40k–80kTiming chain wear, carbon buildup£500–£1,200£2,500–£5,000

Good Value — refined four‑cylinder petrol.

M256.930 (CLS 450)50k–90kEQ Boost system, turbo wear, coolant leaks£800–£2,000£3,500–£6,500

Best Petrol — silky inline‑six, premium costs.

M256.930 (AMG CLS 53)30k–60kTurbo wear, cooling system, EQ Boost£1,000–£2,500£4,500–£8,500

AMG Tax — high performance, high running costs.

OM654.920 (CLS 220 d)80k–150kInjector seal leaks, DPF clogging£400–£1,200£2,800–£4,800

Best Diesel — efficient, durable, Mercedes‑developed.

OM654 M (CLS 300 d)60k–100kAdBlue system, EGR cooler£500–£1,500£3,000–£5,200

Modern Diesel — facelift tech, reliable.

OM656.929 (CLS 350 d / 400 d)60k–120kAdBlue/SCR issues, twin‑turbo wear£800–£2,000£3,200–£6,000

Six‑Cylinder Diesel — refined but complex.

The C257 rule

A £2,800–£4,800 OM654 recon against a £15,000–£40,000 C257 sits at 7–32% of the car's value — comfortably within our 70% Mercedes threshold, making replacement a sensible decision. Against a higher‑mileage CLS 350 d with the OM656, the same maths is still favourable (8–40%). Value the car first, but the C257's strong retained values make most engine replacements economically viable.

Key Takeaways

Which C257 Costs Least To Own?
CLS 220 d (OM654) — best balance of economy and reliability.
Which C257 Costs Most To Own?
AMG CLS 53 (M256) — high‑performance running costs add up.
Which C257 Is Best Value?
CLS 220 d (OM654) — the sweet spot in the range.

Common Problems

01

OM654

Injector Seal Leaks (Black Death)

Affected models:

CLS 220 d (OM654)

Typical failure mileage:

60,000–120,000 miles

Root cause:

The injector seals on the OM654 can fail, allowing combustion gases to escape past the injector. This creates a carbon buildup that sounds like a ticking noise and can eventually damage the cylinder head.

Tiered Cost Table

Our Recommendation

If you hear a ticking noise from the engine bay, have the injector seals checked immediately — a £400–£1,000 repair is far cheaper than the £2,800–£4,800 replacement that follows if the head is damaged.

Compare OM654 engine prices for your C257 diesel

02

M256

EQ Boost System & Coolant Leaks

Affected models:

CLS 450, AMG CLS 53 (M256)

Typical failure mileage:

50,000–90,000 miles

Root cause:

The M256's 48V mild‑hybrid system and coolant system components can develop issues over time — water pump failures and coolant leaks are the most common reported problems.

Tiered Cost Table

Our Recommendation

On CLS 450 and AMG CLS 53 models, have the coolant system and EQ Boost components inspected at 60,000 miles — a £600–£1,200 repair is cheap insurance against a £3,500–£6,500 engine replacement.

Compare M256 engine prices for your C257 petrol

03

OM656

AdBlue/SCR System Issues

Affected models:

CLS 350 d, CLS 400 d (OM656)

Typical failure mileage:

60,000–120,000 miles

Root cause:

The OM656's AdBlue and SCR (selective catalytic reduction) system can suffer from sensor failures and crystallisation, leading to warning lights and potential limp‑home mode.

Tiered Cost Table

Our Recommendation

If your CLS 350 d or 400 d shows an AdBlue warning, have the system inspected immediately — a £400–£1,000 repair is far cheaper than the £3,200–£5,500 replacement that follows if the system fails catastrophically.

Compare OM656 engine prices for your C257 diesel

C257 Engine Replacement Costs — By Engine and Condition

VariantEngine CodeUsed (Supply)Reconditioned (Supply)Rebuilt (Supply)Labour Hours

CLS 350 / CLS 350 4MATICM264.920£1,200–£2,800£2,500–£5,000£4,000–£6,50010–14 hrs

CLS 450 4MATICM256.930£2,000–£3,800£3,500–£6,500£5,500–£8,50012–16 hrs

AMG CLS 53 4MATIC+M256.930 (AMG)£2,800–£4,800£4,500–£8,500£6,500–£10,00014–18 hrs

CLS 220 dOM654.920£1,500–£2,800£2,800–£4,800£4,000–£6,50010–14 hrs

CLS 300 d 4MATICOM654 M£1,800–£3,200£3,000–£5,200£4,500–£7,00010–14 hrs

CLS 350 d 4MATICOM656.929£1,800–£3,200£3,200–£5,500£4,500–£7,50012–16 hrs

CLS 400 d 4MATICOM656.929 (high-output)£2,000–£3,500£3,500–£6,000£5,000–£8,00012–16 hrs

No Generation variance from the Model Page's baseline figures — the C257 shares its MRA platform with the E‑Class (W213), so engine‑bay access and labour times are consistent across the range. Costs are inherited directly per the Authority Model, with no divergence note required.

Core Variants

Diesel Variants

CLS 220 dCLS 300 d 4MATICCLS 350 d 4MATICCLS 400 d 4MATIC

Petrol Variants

CLS 350CLS 350 4MATICCLS 450 4MATICAMG CLS 53 4MATIC+

Scope note: All variants listed are C257 four‑door coupé only. The CLS was discontinued after the C257 generation, with no direct successor planned.

Core Variants

Diesel Variants

CLS 220 dCLS 300 d 4MATICCLS 350 d 4MATICCLS 400 d 4MATIC

Petrol Variants

CLS 350CLS 350 4MATICCLS 450 4MATICAMG CLS 53 4MATIC+

Scope note: All variants listed are C257 four‑door coupé only. The CLS was discontinued after the C257 generation, with no direct successor planned.

Market Intelligence

Most Requested E90 Engines (2025)

1.1. OM654 (2.0 diesel) — most‑requested across the Mercedes range [MB‑VERIFIED]
2.2. M256 (3.0 inline‑six petrol) — strong demand for the CLS 450
3.3. M264 (2.0 petrol) — popular entry‑level choice

Most Requested E90 Variants

1.1. CLS 220 d
2.2. CLS 450 4MATIC
3.3. AMG CLS 53

Average E90 Replacement Cost

£2,500–£8,500 supply only [MB‑QUOTE]

Most Common E90 Failures

1.1. OM654 injector seal leaks (Black Death)
2.2. M256 EQ Boost system/coolant leaks
3.3. OM656 AdBlue/SCR system issues

Live Feed

VehicleLocationIssueEnquiries

Mercedes CLS 220 d C257 (OM654)

London

Ticking noise from engine bay, suspected injector seal leak

5

enquiries

Mercedes CLS 450 C257 (M256)

Birmingham

Coolant loss, water pump failure

4

enquiries

Mercedes AMG CLS 53 C257 (M256)

Manchester

EQ Boost system warning, suspected 48V battery issue

3

enquiries

Updated Monthly

FAQ

BMW 3 Series E90 rear three-quarter view

Why UK Mercedes C257 Owners Trust MercedesEngines.uk

Trusted C257 Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated, and reviewed by real Mercedes owners, as part of the Engine Finders network.
Compare C257 Engine Replacement Companies
see prices, warranty terms, and supply & fit options side‑by‑side before you commit.
UK Engine Replacement Services for C257
covering every variant from CLS 220 d to AMG CLS 53, with supply‑only or full supply & fit available nationwide.

Find the best Mercedes C257 engine replacement UK drivers rely on. Compare real prices from trusted specialists on EnginesMarket today and get back on the road with confidence.

Compare Mercedes CLS C257 Engine Prices on EnginesMarket

Why UK Mercedes C257 Owners Trust MercedesEngines.uk

Trusted C257 Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated, and reviewed by real Mercedes owners, as part of the Engine Finders network.
Compare C257 Engine Replacement Companies
see prices, warranty terms, and supply & fit options side‑by‑side before you commit.
UK Engine Replacement Services for C257
covering every variant from CLS 220 d to AMG CLS 53, with supply‑only or full supply & fit available nationwide.

Find the best Mercedes C257 engine replacement UK drivers rely on. Compare real prices from trusted specialists on EnginesMarket today and get back on the road with confidence.

Compare Mercedes CLS C257 Engine Prices on EnginesMarket

Mercedes CLS C257 Engines — The Complete UK Guide

Mercedes CLS C257 Engine Codes — The Complete Database

Mercedes CLS C257 — Overview

Mercedes CLS C257 — Overview

Best & Worst Engines

Mercedes CLS C257 — Ownership Economics

Common Problems

C257 Engine Replacement Costs — By Engine and Condition

Core Variants

Core Variants

Market Intelligence

FAQ

Why UK Mercedes C257 Owners Trust MercedesEngines.uk

Why UK Mercedes C257 Owners Trust MercedesEngines.uk