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Mercedes GLS 450/580 SPECIALISTS

Mercedes Benz GLS Class 450/580 Engine Replacement Compare Prices & Get Quotes

Get quotes today from trusted UK Mercedes Benz GLS Class 450 and 580 engine specialists. Compare prices on reconditioned, rebuilt and used engines for the 3.0-litre straight-six mild hybrid and the 4.0-litre V8 biturbo - supply & fit available nationwide.

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Mercedes Benz GLS Class 450/580 Engine
from£5,200 to £10,50...
  • Usedfrom £2,800
  • Reconditionedfrom £5,200
  • Common codesM256, M256.930, M176
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3 Simple Steps to Finding the Right Replacement Engine

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Variant History

Mercedes Benz GLS Class 450/580 Engine History & Specs at a Glance

The GLS 450 and 580 launched with the all-new X167 generation in 2019, representing a major technological leap for Mercedes' full-size luxury SUV. The GLS 450 introduced the M256 3.0-litre turbocharged straight-six with 48V EQ Boost mild-hybrid technology - a return to inline-six architecture that delivered unparalleled smoothness. The GLS 580 debuted the M176 4.0-litre twin-turbo V8 with cylinder deactivation and integrated starter-generator, offering effortless V8 performance with improved efficiency.

Mercedes Benz GLS Class 450/580
  1. 2019

    M256, 3.0L turbocharged straight-six with 48V ISG, 367hp (GLS 450, X167)

  2. 2019

    M176.980, 4.0L twin-turbo V8 with 48V ISG, 489hp (GLS 580, X167)

  3. 2023

    Facelift X167; M256 and M176 continue with refined software and emissions systems

Every engine fitted to the Mercedes Benz GLS Class 450 and 580 is covered below, with UK rebuilt pricing and known failure points - from M256 wiring harness degradation and ISG coupling wear to M176 oil separator and rear main seal issues.

Engine Codes & Pricing

Mercedes Benz GLS Class 450/580 Engine Codes Specifications & Replacement Cost

Find your exact engine code, specs and UK replacement cost guide.

M256 — 3.0L Turbocharged Straight-Six with 48V MHEV (2019-present) engine

M256 — 3.0L Turbocharged Straight-Six with 48V MHEV (2019-present)

Power Output
367 hp (270 kW) @ 5,500-6,100 rpm
Torque
500 Nm @ 1,600-4,500 rpm
Years Fitted
2019-present
Displacement
2,999cc
Cylinders
Inline 6, DOHC, 24-valve, turbocharged with electric auxiliary compressor
Engine Code
M256, M256.930

Can’t find your exact engine code?

-> Get quotes for M256 Mercedes GLS 450 engine replacement

Common Problems

Mercedes Benz GLS Class 450/580 Engine Problems Repair Cost vs Replacement

The GLS 450's M256 straight-six and the GLS 580's M176 V8 represent the pinnacle of Mercedes petrol engineering - sophisticated, powerful, and refined. However, both have well-documented weaknesses that can lead to significant repair costs. The M256's wiring harness is prone to heat degradation, while the M176 suffers from oil separator and rear main seal failures. Every rebuilt engine supplied through EnginesMarket includes upgraded components addressing the original failure point, plus a minimum 12-month unlimited-mileage warranty.

Common failure points and repair options

M256 Engine Wiring Harness Degradation

Affected
Mercedes GLS 450 4MATIC (M256, 2019-present)
Typical failure mileage
40,000-80,000 miles
Root cause
The M256's ignition coil wiring harness sits close to the turbocharger and exhaust manifold. Prolonged exposure to engine heat causes the insulation to prematurely deteriorate, leading to exposed wires contacting each other. This condition has caused intermittent check engine lights and electrical system failures. The wiring harness can also disintegrate during routine spark plug replacement work.

Repair options

Repair tierDealer priceSpecialist price
Diagnostics - Wiring harness inspection£200-£400£150-£300
Intermediate - Ignition coil harness replacement£800-£1,500£500-£900
Major - Full engine wiring harness replacement£2,500-£4,500£1,800-£3,000
Full Replacement - Rebuilt M256 engine£8,500-£12,000£5,200-£8,800
Our recommendation
The M256's wiring harness is a known weak point - regular inspection is recommended, especially if you experience misfires or engine warning lights. Replacing the ignition coil harness section at £500-£900 is significantly cheaper than a full engine harness replacement. However, if the wiring harness has caused ECU damage, a full rebuilt engine with a new harness is the only safe option. On a GLS 450 worth £35,000-£60,000, this is a justifiable investment.
-> Compare rebuilt M256 Mercedes GLS 450 engine prices

M256 48V ISG & Timing Chain Issues

Affected
Mercedes GLS 450 4MATIC (M256, 2019-present)
Typical failure mileage
40,000-80,000 miles
Root cause
The M256's 48V integrated starter-generator (ISG) coupling can wear on early X167 models, causing charging system failures and warning lights. Timing chain rattle on cold starts has also been reported at higher mileage - the chain stretches and the tensioner fatigues, causing a "clattering" or "rattling" sound on cold starts.

Repair options

Repair tierDealer priceSpecialist price
Minor - 48V system diagnostics£200-£400£150-£300
Intermediate - 48V battery/ISG replacement£2,200-£3,500£1,800-£2,500
Intermediate - Timing chain tensioner replacement£800-£1,200£500-£800
Major - Full timing chain replacement£3,000-£5,000£2,000-£3,500
Full Replacement - Rebuilt M256 engine£8,500-£12,000£5,200-£8,800
Our recommendation
If your GLS 450 displays a 48V warning or experiences a no-start condition, do not assume a conventional jump start will work - the 48V system is separate from the 12V starter battery. Specialist diagnostics are essential. For timing chain rattle, if caught early with no fault codes, tensioner replacement is cost-effective. Once chain skip triggers camshaft correlation codes, the full timing chain kit is mandatory. On a GLS 450 worth £35,000-£60,000, preventative maintenance is always the better investment.
-> Compare M256 Mercedes GLS 450 engine quotes

M176 Oil Separator & Rear Main Seal Failure

Affected
Mercedes GLS 580 4MATIC (M176.980, 2019-present)
Typical failure mileage
40,000-80,000 miles
Root cause
The M176/M177 engine family can suffer from oil-vapour separator (PCV) blockage. When the separator becomes blocked, crankcase pressure increases, and the weakest point in the crankcase seal system - the rear main crankshaft oil seal (RMS) - fails. Oil leaks from the rear of the engine, often dripping onto the transmission bellhousing. This issue has been reported across multiple M176/M177 applications.

Repair options

Repair tierDealer priceSpecialist price
Diagnosis - Oil separator/PCV check£200-£400£150-£300
Intermediate - Oil separator replacement£800-£1,200£500-£800
Major - Rear main seal replacement£3,500-£5,000£2,500-£3,500
Full Replacement - Rebuilt M176 engine£12,000-£18,000£6,000-£10,500
Our recommendation
The oil separator is the root cause of most M176 rear main seal leaks. If you notice oil around the transmission bellhousing or a burning oil smell, have the crankcase pressure checked immediately. If caught early, replacing the oil separator alone (£500-£800 at a specialist) prevents the much more expensive rear main seal replacement. If the rear main seal has already failed, replacing both the seal and the oil separator together is the only sensible approach. On a GLS 580 worth £45,000-£75,000, the full rebuilt engine route is justifiable if bottom-end damage has occurred.
-> Compare rebuilt M176 Mercedes GLS 580 engine prices

M176 Turbocharger Bearing Wear & Rough Idle

Affected
Mercedes GLS 580 4MATIC (M176.980, 2019-present)
Typical failure mileage
50,000-90,000 miles
Root cause
The M176's twin-turbochargers are mounted in the hot-vee configuration, subjecting them to extreme heat. Sustained high-temperature operation accelerates bearing wear, leading to oil burning and potential turbo failure. Rough idle and vibration have also been reported on GLS 580 models, with some owners experiencing shaking at idle that persisted despite engine mount replacements and fuel injector work.

Repair options

Repair tierDealer priceSpecialist price
Diagnostics - Turbocharger inspection£200-£400£150-£300
Intermediate - Single turbocharger replacement£2,500-£4,000£1,800-£3,000
Major - Both turbochargers replacement£4,500-£7,000£3,500-£5,500
Full Replacement - Rebuilt M176 engine£12,000-£18,000£6,000-£10,500
Our recommendation
Preventative maintenance is the key to avoiding M176 turbocharger failure. Use only Mercedes-spec oil (MB 229.5) and change it every 10,000 miles or 12 months - never stretch the interval. If you hear a high-pitched whistle, notice a loss of power, or experience rough idle, have the turbochargers inspected immediately. If one turbo has failed, replace both - the other will typically fail within a short period due to shared oil supply and similar operating conditions.
-> Compare M176 Mercedes GLS 580 engine quotes

Don't Let Wiring Harness Degradation, Oil Separator Failure, or Turbo Issues Write Off Your Mercedes GLS 450 or 580

Whether you're facing M256 wiring harness degradation on your GLS 450, 48V system issues, or M176 oil separator failure on your GLS 580, EnginesMarket makes it simple to compare quotes from trusted UK Mercedes petrol specialists. Every rebuilt engine in our network carries upgraded components addressing the original design weakness - improved wiring harnesses, reinforced oil separators, and bench-tested turbos - plus a minimum 12-month unlimited mileage warranty with nationwide delivery and supply & fit options. Don't pay main dealer premiums. Compare prices from independent Mercedes specialists who know these sophisticated petrol engines inside out.

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FAQ

Mercedes Benz GLS Class 450/580 Engine ReplacementFrequently Asked Questions

Everything Mercedes Benz GLS Class 450/580 owners usually ask before choosing a rebuilt, reconditioned or used replacement engine.

Why Choose Us

Compare Mercedes GLS Class 450/580 Engine Prices Today

Comparing quotes for your Mercedes GLS 450 or 580 is completely free, with no obligation and no pressure. Enter your registration above to get tailored quotes from UK Mercedes petrol specialists who understand the M256 straight-six and M176 V8 inside out. Whether you need a used engine, a reconditioned unit, or a full rebuilt engine with upgraded wiring harnesses, oil separators, and turbo components, we'll connect you with the right specialist for your exact GLS - with a minimum 12-month warranty on every engine supplied.

200+200+ M256 and M176 engines supplied through our network
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