Mercedes-Benz SLK Common Problems & Known Faults (UK)
If you are considering buying a used Mercedes-Benz SLK, there are several major reliability issues worth knowing about first. Our garage database tracks 7 known faults for this model, 4 of them rated high severity. Every one below is a repair bill a seller has good reason not to mention.
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Generation 1 of 25 known faults · 10 owner reports · 18 good notes
Mercedes-Benz SLK R170 (1996 to 2004) problems
Engine/EmissionsHigh severity📝 Editorial
Soft metal on the balance shaft timing gear wears completely away, destroying engine timing
Rough guide
£2000-4000
Typical symptoms
Engine Management Light (EML) on
fault codes P0016 / P0017 (camshaft timing)
rough running or misfiring
Affected vehicles
Engines:
3.5 V6 Petrol (M272) / 5.5 V8 (M273)
Typical mileage:
60000-90000 miles
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Engine/EmissionsHigh severity📝 Editorial
Single-row timing chain stretches and jumps teeth, destroying the valves
Rough guide
£1500-2500
Typical symptoms
loud metallic rattle on startup for 3-5 seconds
engine management light
loss of compression and non-start
Affected vehicles
Engines:
1.8 Kompressor / CGI Petrol (M271)
Typical mileage:
60000-90000 miles
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OtherMedium severity💬 3 owner reports, 2014
Severe corrosion, particularly affecting wheel arches, door handles, and boot lid. This is a common issue across Mercedes models from this era.
Rough guide
£500-1500+
Typical symptoms
Visible rust bubbles on wheel arches
Corrosion around door handles
Rust on boot lid edges
Affected vehicles
Engines:
All R170 models
Typical mileage:
70000-120000 miles
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ElectricalHigh severity💬 3 owner reports, 2014
Failure of the complex folding hardtop roof and window mechanism, often due to sensor issues or hydraulic pump failure. Repairs can be prohibitively expensive on older cars.
Rough guide
£1000-3000+
Typical symptoms
Roof fails to open or close fully
Windows do not drop or raise correctly during roof operation
Roof mechanism jams or makes unusual noises
Affected vehicles
Engines:
All R170 models
Typical mileage:
60000-100000 miles
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Engine/EmissionsMedium severity📝 Editorial
Failure of the right-side pre-catalytic converters and main catalytic converters is common on the SLK320 V6. Mercedes main dealer replacement costs are very high.
Rough guide
£1400-2000
Typical symptoms
Reduced engine performance
Check engine light illuminated
Rattling noise from exhaust system
Failed MOT emissions test
Affected vehicles
Engines:
3.2 V6 (SLK320) petrol
Typical mileage:
80000-120000 miles
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What owners report on the R170
10 single reports, unconfirmed
One owner each, in their own words rewritten as a line, and not counted in our risk scoring. A fault joins the list above once a second report or an editorial source backs it.
Bodywork · June 2017Lacquer peeled from the metallic red paint on a 2010 SLK 200K, which was found to have been poorly resprayed previously.
Suspension and steering · March 2017A 2005 SLK350 experienced multiple spring and damper failures by 68,000 miles, including a broken front coil spring.
Gearbox and clutch · April 2015A 2009 SLK200 with 40,000 miles developed a grinding noise from the rear differential, with metal shards found in the oil.
Interior · April 2015A centre console lid that would not open on both sides was fixed by enlarging the holes for the locking pins.
Gearbox and clutch · March 2014The gear linkage on a 2009 SLK 200K manual with 17,000 miles failed due to a missing circlip, with repair costs quoted.
Electrics · October 2013Blocked bulkhead vent drains on a 2008 SLK caused rainwater to flood the heater motor, costing £800 to repair.
Gearbox and clutch · May 2013The clutch slave cylinder on a manual model is located inside the bellhousing, making its replacement a costly labour job of around £500.
Electrics · November 2012A 2006 SLK350 with 49,000 miles had numerous electrical faults, including a stuck driver's window and transmission issues, costing over £3,000.
Interior · October 2012The air conditioning compressor on a 2005 SLK failed at 40,000 miles, with a replacement cost of £1,600.
Bodywork · February 2012This car experienced water ingress through its roof and boot lid sealing components.
What owners like about the R170
18 notes
This model received a strong four-star rating for occupant protection in 2002 NCAP assessments.
Mercedes recorded the fifth lowest average expenditure on warranty claims for cars up to ten years old in 2002.
The model generally had the ninth lowest average warranty repair costs in the 2003 Warranty Direct Reliability index.
Fewest problems and faults were reported, with an average number of breakdowns in a 2003 Which survey.
This model earned a four-star crash safety rating in 2002 NCAP tests, with low warranty claim expenses.
The second-generation SLK is a desirable car with a folding hardtop, offering a more practical and liveable experience than some rivals.
The facelifted model features 650 new parts, including updated styling, a modified interior, and more economical engines with increased output.
The new NTG 2.5 audio and telematics system is user-friendly, offering Bluetooth hands-free and a media interface for mobile devices.
The 305PS SLK350 automatic model now produces under 225g/km of CO2 emissions.
The SLK 350 engine offers increased power and torque, with the 7G-TRONIC automatic transmission providing automatic throttle blipping on downshifts.
The four-cylinder supercharged engine was boosted to 184 hp, with torque increased to 250 Nm, while reducing fuel consumption and CO2 emissions.
The SLK 55 AMG is equipped with a 5.5-litre V8 engine producing 360 hp and 510 Nm of torque.
New SLK models feature a precise six-speed manual gearbox as standard, with automatic transmissions available as options.
A newly developed direct steering system, available as an option, enhances agility and manoeuvrability while maintaining high-speed stability.
The direct-steer system uses a new rack with slick gearing, reducing steering wheel revolutions from lock to lock by about 25 percent.
The 2008 SLK 55 AMG features sharpened handling dynamics and new direct steering with variable servo assistance for improved agility.
The improved SLK350 manual, available from April 2007, offers good acceleration, pleasing sound, and feels secure when driven quickly.
The SLK 2LOOK Edition, launched June 2009, features distinctive paint options, 18-inch alloy wheels, and a luxurious black and white leather interior.
Generation 2 of 22 known faults · 3 owner reports · 3 good notes
Mercedes-Benz SLK R172 (2011 to 2015) problems
OtherMedium severity💬 6 owner reports, 2015 to 2017
Widespread problem with microblistering and peeling lacquer on Mars Red and Fire Opal Red paint finishes, particularly on cars built between 2011 and 2015. This often requires a full bare-metal respray.
Rough guide
£2000-4000+
Typical symptoms
Tiny paint blisters appearing all over the bodywork
Peeling lacquer, especially on bumper valances
Blistering worse at low temperatures, disappearing when hot
Affected vehicles
Engines:
Mars Red / Fire Opal Red paint finishes
Typical mileage:
10000-50000 miles
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OtherHigh severity💬 3 owner reports, 2018 to 2020
The colour-coded roof panels on either side of the glass roof can delaminate, allowing water to enter under the roof and leak into the cabin, soaking seats and carpets. This roof material was reportedly discontinued in 2013 due to this problem.
Rough guide
£600-1000+
Typical symptoms
Water puddles on seats or soaked carpets
Damp interior smell
Visible delamination or bowing of roof panels in hot weather
Roof 'coming away at the back in sunshine'
Affected vehicles
Engines:
All R172 models with specific roof material
Typical mileage:
30000-80000 miles
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What owners report on the R172
3 single reports, unconfirmed
One owner each, in their own words rewritten as a line, and not counted in our risk scoring. A fault joins the list above once a second report or an editorial source backs it.
Electrics · April 2017A 2013 SLK350 with 19,700 miles experienced multiple electrical problems, including new RPM and NOX sensors, a heater box, and an aerial.
Electrics · March 2017The driver's door lock of a 2013 SLK AMG became stuck, with the dealer attempting to charge for a diagnostic despite warranty coverage.
Bodywork · February 2017A 2013 Mercedes SLK purchased in 2016 had paint problems, with the dealer offering a respray or replacement, but not a like-for-like exchange.
What owners like about the R172
3 notes
A broad range of engines are available, including a turbodiesel, all of which can be paired with Mercedes' excellent seven-speed automatic gearbox.
The SLK is well-suited for grand touring due to its comfortable ride and relaxed nature, with a quick-folding metal roof.
The SLK includes a comprehensive list of standard safety equipment, with additional options available to enhance protection.
Sellers rarely admit these faults outright
We track 21 specific phrases sellers use in adverts to soft-pedal these exact issues. Paste any Mercedes-Benz SLK advert and we check it in seconds.
Mercedes-Benz SLK service intervals: cambelt, chain and gearbox oil
An overdue cambelt is the most expensive thing a seller can fail to mention on a used SLK. These are the figures UK specialists work to.
Timing chainChain
W203, W204, W211, 1.8 KOMPRESSOR, M271
No fixed replacement interval
Single-row timing chain notoriously stretches, jumping teeth and destroying the engine. Listen for 3-5 second metallic rattle on cold start. Often replaced between 60k-90k miles.
Automatic gearbox oil
7G-TRONIC, 722.9, 7 SPEED
40,000 miles or 4 years, whichever comes first
Mercedes initially claimed 'filled for life', which specialists call marketing over engineering. The recommendation is a fluid and filter change every 40,000 miles to prevent conductor plate failure, a GBP 800-1,200 repair. Some sources suggest 60,000 miles, so the shorter figure is recorded.
Automatic gearbox oil
722.6, 5G-TRONIC, 5 SPEED
40,000 miles
Officially 'sealed for life' but independent specialists recommend ATF (MB 236.14 spec, which supersedes 236.10 and 236.12) and filter changes every 40,000 miles to head off valve body and conductor plate trouble. Capacity is about 7.5 litres. Fitted to most pre-2011 rear-wheel-drive Mercedes including the pre-2010 C, E and SLK.
Always confirm against the vehicle handbook. Intervals vary by engine, and several manufacturers revised theirs after failures in service.
Repair costs are typical UK ranges, not quotes. Actual cost depends on condition and garage.Data last verified: September 2026
Mercedes-Benz SLK buying questions
Is a used Mercedes-Benz SLK reliable?
The Mercedes-Benz SLK has 7 known faults in our database across 2 generations, 4 of them rated high severity. The most serious are electrics (failure of the complex folding hardtop roof and window mechanism) and engine (soft metal on the balance shaft timing gear wears completely away). None of them makes the car a bad buy on its own; the risk is a seller who knows and says nothing.
What are the most common Mercedes-Benz SLK problems?
Three stand out. Electrics: failure of the complex folding hardtop roof and window mechanism (typically 60000 to 100000 miles). Engine: soft metal on the balance shaft timing gear wears completely away, destroying engine timing (typically 60000 to 90000 miles). Engine: single-row timing chain stretches and jumps teeth, destroying the valves (typically 60000 to 90000 miles). The full list above is grouped by generation, with typical mileage and a rough repair cost for each.
Which Mercedes-Benz SLK years should I avoid?
No Mercedes-Benz SLK year is a write-off, but the R170 (1996 to 2004) carries the most serious faults: electrics and engine. The R172 (2011 to 2015) has high-severity faults on record too. Year matters less than whether the specific car has had the known fixes, so check the history for them.
What should I check when viewing a used Mercedes-Benz SLK?
Ask the seller about the electrics and engine faults on this page and whether they have been fixed, with invoices. On the test drive watch for roof fails to open or close fully, engine Management Light (EML) on and loud metallic rattle on startup for 3-5 seconds. Read the MOT history for repeat advisories, then paste the advert into the free check, which reads it against all 7 known faults before you travel. Check a Mercedes-Benz SLK advert →
What is the real MPG of a Mercedes-Benz SLK?
Owners report 35.0 mpg on average across the Mercedes-Benz SLK engines with data, about 86% of the official combined figure. The gap between official and real-world economy varies a lot by engine, so the Real MPG page lists every engine and generation separately, from 518 owner submissions. Mercedes-Benz SLK Real MPG by engine →
Where this Mercedes-Benz SLK fault data comes from
If you used to check the Honest John “Good & Bad” section before the site closed in 2026, this page is where that information now lives. We rebuilt the Mercedes-Benz SLK owner-report history from the archived Honest John dataset, added our own research, specialist and owner-club sources and DVSA recall data, and we keep it free. Each fault above is badged with its source. The same data feeds our free advert check, which reads a listing against every known fault for the exact engine and year.
Knowing what a Mercedes-Benz SLK goes wrong with is half of it. The rest is reading the advert and checking the car's history before you hand any money over.