Mercedes Benz GLS Class 450/580 Engine ReplacementCompare 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.
Supply & Fit Available
12-Month Warranty
Nationwide Delivery
100+ Suppliers
From £5,200 to £10,500
Used from £2,800 · Reconditioned from £5,200 · Common codes: M256, M256.930, M176, M176.980
From £2,800
Tested, bare/short engine
From £5,200
Rod bearings addressed, tested
From quote
Upgraded bearings, full teardown, revised valvetrain
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3 Simple Steps3 Simple Stepsto Finding the Best Mercedes Benz GLS Class 450/580 Replacement Engineto Finding the Best Mercedes Benz GLS Class 450/580 Replacement Engine
Most replacements completed within 3-5 days.
Variant HistoryMercedes 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.
Variant HistoryMercedes 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
Fuel TypePetrol (M256: 48V mild-hybrid straight-six; M176: 48V mild-hybrid V8)
Engine Size Range3.0L-4.0L (M256: 2,999cc; M176: 3,982cc)
Power Output Range367-489hp across the variant's historyEngine History Timeline
M256 3.0L turbocharged straight-six with 48V ISG, 367hp (GLS 450, X167)
M176.980 4.0L twin-turbo V8 with 48V ISG, 489hp (GLS 580, X167)
Facelift X167; M256 and M176 continue with refined software and emissions systems
Key Specs Snapshot
Fuel TypePetrol (M256: 48V mild-hybrid straight-six; M176: 48V mild-hybrid V8)Engine Size Range3.0L-4.0L (M256: 2,999cc; M176: 3,982cc)Power Output Range367-489hp across the variant's historyYears Produced2019-presentEvery 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.
Mercedes Benz GLS Class 450/580 Engine Codes - Specifications & Replacement CostMercedes Benz GLS Class 450/580 Engine Codes - Specifications & Replacement Cost
3.0L Turbocharged Straight-Six with 48V MHEV (2019-present)
Power Output367 hp (270 kW) @ 5,500-6,100 rpmTorque500 Nm @ 1,600-4,500 rpmYears Fitted2019-presentDisplacement2,999ccCylindersInline 6, DOHC, 24-valve, turbocharged with electric auxiliary compressorEngine CodeM256, M256.930
Compatible Trim Levels
- GLS 450 4MATIC
- GLS 450 4MATIC AMG Line
- GLS 450 4MATIC Premium Plus
Find your exact engine code, specs and UK replacement cost guide.
Used
Tested, ready-to-fit engine
£2,800-£4,200
Reconditioned
Addressed known issues, tested
£4,800-£6,500
Rebuilt
Full teardown, upgraded internals
£5,200-£8,800
Common Failure
Engine wiring harness degradation - the ignition coil wiring harness sits close to the turbocharger and exhaust manifold, and heat cycling can cause insulation to melt, leading to misfires and check engine lights. 48V ISG coupling wear has also been reported on early X167 models, along with timing chain rattle on cold starts at higher mileage. Typical failure mileage: 40,000-80,000 miles.
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.
The Straight-Six's Electrical Achilles' Heel
Affected Vehicles
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.
Why It Happens
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.
Dealer (parts + labour)
£200-£400
Specialist (parts + labour)
£150-£300
What it involves
Visual inspection of engine wiring harness, particularly near ignition coils
Suitability
If warning lights or misfires occur
1 - 2 daysDealer (parts + labour)
£800-£1,500
Specialist (parts + labour)
£500-£900
What it involves
Replace ignition coil wiring harness section, inspect connectors
Suitability
If harness damage is localised
1 - 2 daysDealer (parts + labour)
£2,500-£4,500
Specialist (parts + labour)
£1,800-£3,000
What it involves
Replace complete engine wiring harness, ECU reprogramming
Suitability
If widespread harness damage or ECU faults present
1 - 2 daysDealer (parts + labour)
£8,500-£12,000
Specialist (parts + labour)
£5,200-£8,800
What it involves
Supply & fit rebuilt M256 with new wiring harness, 12-month warranty
Suitability
If electrical failure has caused engine damage
1 - 2 daysAll prices are indicative UK market ranges based on current UK specialist supplier data.| Repair Tier | Dealer (Parts + Labour) | Specialist (Parts + Labour) | What It Involves | Suitability | Estimated Time |
|---|---|---|---|---|---|
 Diagnostics - Wiring harness inspection Minor | £200-£400 | £150-£300 | Visual inspection of engine wiring harness, particularly near ignition coils | If warning lights or misfires occur | 1 - 2 days |
 Intermediate - Ignition coil harness replacement Best Value | £800-£1,500 | £500-£900 | Replace ignition coil wiring harness section, inspect connectors | If harness damage is localised | 1 - 2 days |
Major - Full engine wiring harness replacement Best Value | £2,500-£4,500 | £1,800-£3,000 | Replace complete engine wiring harness, ECU reprogramming | If widespread harness damage or ECU faults present | 1 - 2 days |
Full Replacement - Rebuilt M256 engine Best Value | £8,500-£12,000 | £5,200-£8,800 | Supply & fit rebuilt M256 with new wiring harness, 12-month warranty | If electrical failure has caused engine damage | 1 - 2 days |
Vehicle Value Check
Vehicle Value Check
A typical 2019-present GLS 450 4MATIC is worth approximately £35,000-£60,000 depending on mileage and condition. The GLS 450 sits firmly in the £15,000+ band - replacement cost is small relative to vehicle value.
Our Recommendation
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.
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.
Compare rebuilt M256 Mercedes GLS 450 engine prices
12-Month Minimum
UK Specialists Vetted
Best Price GuidanceImportant Information
Important Information
"All prices are indicative UK market ranges based on historical quote data and repair requests from our network of engine specialists. Dealer pricing is estimated based on published main dealer labour rates and genuine OEM parts pricing. Specialist pricing reflects actual quote data from EnginesMarket's UK network. Actual costs vary depending on damage severity, vehicle condition, variant, and workshop location within the UK. Use our free comparison tool to get tailored quotes for your specific Mercedes GLS Class 450 or 580. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited mileage warranty - always confirm exact terms with your chosen supplier."
Mercedes Benz GLS Class 450/580 Engine ReplacementFrequently Asked Questions
Question 1How much does a Mercedes GLS 450 or 580 engine replacement cost in the UK-
Short summary: A rebuilt M256 engine for the GLS 450 costs £5,200-£8,800 supply-only; a rebuilt M176 V8 engine for the GLS 580 costs £6,000-£10,500 supply-only. Fitting adds £1,200-£2,500 depending on complexity - both MHEV and V8 work requires specialist knowledge.
- GLS 450 (M256): rebuilt unit £5,200-£8,800; used engine from £2,800
- GLS 580 (M176.980): rebuilt unit £6,000-£10,500; used engine from £3,500
- M256 wiring harness replacement: £500-£900 at specialist
- M176 oil separator replacement: £500-£800 at specialist
Question 2What are the signs of wiring harness failure on a Mercedes GLS 450-
Short summary: The M256's ignition coil wiring harness sits close to the turbocharger and exhaust manifold. Heat causes insulation to deteriorate, leading to check engine lights, misfires, and rough running. The harness can also disintegrate during spark plug replacement.
- Check engine light or multiple warning lights - faulty connections trigger sensor errors
- Engine misfires or rough running - inconsistent electrical signals to ignition coils or injectors
- Starting problems or no start - affected circuits for starter, crankshaft sensor, or fuel system
- Harness deterioration near ignition coil connectors due to heat exposure
Question 3Is the Mercedes GLS 450 engine (M256) reliable-
Short summary: The M256 straight-six is considered one of Mercedes' best modern engines - smooth, refined, and fundamentally reliable. However, it has known wiring harness degradation issues and 48V system vulnerabilities that can lead to expensive repairs. With these addressed, the M256 is proving durable.
- Wiring harness degradation near turbocharger is the most common electrical issue
- 48V ISG and battery failures can cause no-start conditions
- Timing chain rattle on cold starts can occur at higher mileage
- Well-maintained M256 engines exceed 100,000 miles with 0% issues reported by many owners
Question 4Is the Mercedes GLS 580 V8 engine (M176) reliable-
Short summary: The M176 is a powerful and refined V8, but it has known oil separator and rear main seal issues that can lead to significant repair costs. Turbocharger bearing wear and rough idle have also been reported. With proactive maintenance and early intervention, these engines can exceed 100,000 miles.
- Oil separator blockage is the root cause of rear main seal failures
- Turbocharger bearing wear due to hot-vee design heat exposure
- Rough idle and vibration at idle have been reported on some units
- Regular oil changes with MB 229.5 spec oil are essential
Question 5How long do Mercedes GLS 450 and 580 engines last-
Short summary: Properly maintained M256 straight-six engines are showing excellent longevity, with owners reporting 0% engine issues beyond 90,000 miles. The M176 V8 is too new for definitive long-term data, but with proactive maintenance and early intervention on known issues, 100,000-150,000 miles is achievable.
- M256 (450): 100,000+ miles with regular servicing - early reliability is strong
- M176 (580): too early for definitive data - oil separator and turbo issues from 40k-80k miles
- Service interval is 10,000 miles or 12 months - use Mercedes-spec oil (MB 229.5)
- Late oil changes accelerate wiring harness degradation and oil separator failure
Question 6What's the difference between the GLS 450 and GLS 580 engines-
Short summary: The GLS 450 uses the M256 3.0-litre turbocharged straight-six with 48V mild hybrid (367hp). The GLS 580 uses the M176 4.0-litre twin-turbo V8 with 48V mild hybrid (489hp). Both feature EQ Boost, but the V8 delivers significantly more power and torque with cylinder deactivation for efficiency.
- GLS 450: 3.0L straight-six, 367hp, 500Nm torque
- GLS 580: 4.0L V8, 489hp, 700Nm torque
- Both feature 48V ISG with 22hp EQ Boost
- M176 features cylinder deactivation (CAMTRONIC) for improved efficiency
Why Choose UsCompare Mercedes GLS Class 450/580Engine PricesToday
200+ M256 and M176 engines supplied through our network
12-Month Warranty on every rebuilt GLS 450 and 580 engine
Nationwide UK delivery
supply & fit available for straight-six and V8
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.
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