The MOT Files

Known faults, from the test record

Mercedes-Benz SLK common problems

What fails on the Mercedes-Benz SLK at MOT, which parts are behind it, and how each model year compares. From 54,151 DVSA test records.

Data updated

Quick answer

The Mercedes-Benz SLK's most common MOT problems are tyres, suspension bushes, coil springs, recorded in 32.8%, 31.3% and 23.5% of failed tests respectively. By model year, 2016 cars pass most often (82.3%) and 2004 cars least (66.2%), though most of that gap is age. Every figure here is what testers recorded, not what owners reported.

A “common problems” list is usually a forum thread: whoever had the worst day writes the longest post. This one is built the other way, from every Mercedes-Benz SLK that took an MOT last year and what the tester wrote down. It cannot see breakdowns, electrical gremlins or a gearbox that hunts, because the test does not check those. What it can see, it sees across 54,151 cars.

By component

What wears out on a SLK

Failure items grouped by the part behind them, with the share of failed Mercedes-Benz SLK tests recording each. A part can carry several DVSA wordings; they are listed beneath. One failed test often lists several items, so shares do not sum to 100%.

  1. 1.Tyres

    32.8% of failed tests

    Tread wears with every mile and sidewalls age and take kerb damage; the legal minimum is 1.6 mm across the central three-quarters.

    • “Tyre tread depth not in accordance with the requirements” — explained10.9%
    • “A tyre cords visible or damaged” — explained8.3%
    • “A tyre seriously damaged” — explained6.6%
    • “A tyre seriously damaged” — explained4.9%

    Across all cars, tyres failures run at a similar rate at every age, because they are replaced on a cycle rather than wearing out with the car. How long tyres last

  2. 2.Suspension bushes

    31.3% of failed tests

    Rubber bushes in arms and links perish and split with age and load; the most recorded suspension item on the test.

    • “A suspension pin, bush or joint excessively worn” — explained13.3%
    • “A suspension pin, bush or joint excessively worn” — explained6.2%
    • “A suspension joint dust cover missing or no longer prevents the ingress of dirt etc” — explained5.7%
    • “A suspension joint dust cover missing or no longer prevents the ingress of dirt etc” — explained3.9%

    Across all cars, suspension bushes failures climb 20-fold between three and fifteen years, peaking at 15+ years. How long suspension bushes last

  3. 3.Coil springs

    23.5% of failed tests

    Springs fatigue and corrode where the coating chips, then snap, often at the bottom coil; potholes and salt accelerate it.

    • “A spring or spring component fractured or seriously weakened” — explained23.5%

    Across all cars, coil springs failures climb 20-fold between three and fifteen years, peaking at 12–14 years. How long coil springs last

  4. 4.Bulbs and lamps

    15.3% of failed tests

    Filament bulbs simply expire; the cheapest and most avoidable failure on the test, and one of the most recorded.

    • “A lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning” — explained3.8%
    • “Stop lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning” — explained3.8%
    • “A headlamp or light source missing, inoperative or more than ½ not functioning in the case of LED” — explained3.2%
    • “Lamp emitted colour, position or intensity not in accordance with the requirements” — explained2.6%

    Across all cars, bulbs and lamps failures climb 15-fold between three and fifteen years, peaking at 15+ years. How long bulbs and lamps last

  5. 5.Wiper blades and washers

    11.3% of failed tests

    Rubber blades harden and split within a year or two; washer jets block and pumps fail.

    • “Wiper blade missing or obviously not clearing the windscreen” — explained5.0%
    • “Windscreen washers not working or not providing sufficient fluid to clear the windscreen” — explained3.9%
    • “Windscreen washers not working or not providing sufficient fluid to clear the windscreen” — explained2.4%

    Across all cars, wiper blades and washers failures run at a similar rate at every age, because they are replaced on a cycle rather than wearing out with the car. How long wiper blades and washers last

  6. 6.Brake pipes

    10.7% of failed tests

    Steel pipes under the car corrode from salt and moisture, fastest on cars kept outside in wet or coastal areas; failure is for excessive corrosion or damage.

    • “Brake pipe damaged or excessively corroded” — explained9.2%
    • “Leaking brake pipe or connection on a hydraulic system” — explained1.5%

    Across all cars, brake pipes failures climb from nothing between three and fifteen years, peaking at 15+ years. How long brake pipes last

  7. 7.Headlamp aim

    9.1% of failed tests

    Aim drifts with sagging suspension, a knocked lamp or a botched bulb change; adjustment, not a part.

    • “The aim of a headlamp is not within limits laid down in the requirements” — explained5.4%
    • “The aim of a headlamp is not within limits laid down in the requirements” — explained2.3%
    • “The aim of a headlamp is not within limits laid down in the requirements” — explained1.3%

  8. 8.Suspension arms and mountings

    6.2% of failed tests

    Arms bend on impact and mountings corrode into the body; a corroded mounting is a structural item and fails as one.

    • “A suspension component excessively damaged or corroded” — explained4.4%
    • “The strength or continuity of the load bearing structure within 30cm of any sub-frame, spring or suspension component mounting (a 'prescribed area') is significantly reduced or inadequately repaired” — explained1.8%

By registration year

SLK problems by year

MOT pass rate for Mercedes-Benz SLK cars by the year they were first registered, from years with at least 1,000 tests. Every car in a row is the same age, so the rate is raw. Neighbouring years differ by a year of wear — a step of a point or two is age. The step at 2011, up 4.7 points, is larger than wear explains and most likely marks a change in the cars themselves.

199971%
200070%−1.5
200171%+1.4
200271%+0.2
200368%−3.2
200466%−1.7
200568%+1.6
200667%−0.9
200767%+0.4
200868%+0.5
200969%+1.4
201071%+1.3
201175%+4.7
201274%−1.6
201374%+0.6
201476%+2.2
201580%+3.5
201682%+2.3

Last column: change on the previous year, in points. Years registered within the last three years have not yet been tested and are not shown.

Before it fails

What testers warn SLK owners about

Advisories are the same parts a year or two earlier. Share of all Mercedes-Benz SLK tests carrying an advisory for each.

Go deeper

The rest of the SLK file

Common questions

What are the most common problems with a Mercedes-Benz SLK?
Going by what fails the MOT, tyres (recorded in 32.8% of failed tests), suspension bushes (recorded in 31.3% of failed tests), and coil springs (recorded in 23.5% of failed tests). These are the items testers actually record across 54,151 tests, not reports from owners, so they describe what goes wrong at the point where it has to be fixed.
Which Mercedes-Benz SLK year is the most reliable?
By MOT pass rate, Mercedes-Benz SLK cars registered in 2016 do best at 82.3% and 2004 cars do worst at 66.2%. Most of that ordering is simply age — newer cars pass more — so read the year table for steps larger than a couple of points between neighbouring years; those mark a change in the cars rather than the calendar. The largest such step is at 2011, up 4.7 points on 2010.
Is the Mercedes-Benz SLK reliable?
Adjusted for the age and mileage of the cars tested, the Mercedes-Benz SLK passes 69.3% of MOTs against a national 72.3%. An MOT measures roadworthiness on the day rather than breakdowns or running costs, so this is a reliability measure in the narrow sense: how often the car meets the legal standard, and what stops it.
What should I check when buying a used Mercedes-Benz SLK?
Start with what fails most: tyres, suspension bushes, coil springs. Then read the car's own MOT history for advisories carried year to year without repair — the model tells you what to expect, the history tells you whether this owner dealt with it.

Analysis built from DVSA data of