Model Reports 4 min read Updated 18 Oct 2026

Mercedes-Benz CLS 2009: reliability & common MOT faults

In 2025, 66 in every 100 first MOTs on a 2009 Mercedes-Benz CLS were passes. Most common reason for a fail: Suspension arm ball joint (front).

Summary

With 895 first tests, there are too few to say whether the 2009 Mercedes-Benz CLS differs from the model years either side.

At a glance

How 895 first tests went in 2025.

Passed first time
66 in every 100
Did not pass first time
34 in every 100302 failed first-attempt tests
The typical car
16 yearsabout 114,788 miles
First tests counted
895

What failed most often

  1. Suspension arm ball joint (front)19 in every 100 failed tests

How we count this. Data: UK MOT open data, 2025. Only Class 4 cars on their first MOT of the year are counted. A car that fails and is fixed at the test station still counts as a fail in the first-attempt rate. These are raw results, not adjusted for age, mileage, or peer mix. The MOT does not test engine or gearbox internals.

Note:

These are patterns across 2009 Mercedes-Benz CLS vehicles in 2025, not a prediction that any one car will have them. Faults are grouped by part of the car. A wear pattern follows age and use more than the way the car was built. They come from MOT defect codes, not manufacturer bulletins, recalls or a diagnosis of any one car.

Brakes

One fault: rigid brake pipes (rear), 4.9 times as often as on similar cars.

Figures below are measured across the 301 of 302 failed first attempts (99.7%) that recorded an odometer reading in 2025. Mileage is needed to compare like with like.

We only list faults with at least 20 failures and a rate of about 2.0 times that of similar cars, which keeps one-off results out of the list.

Rigid brake pipes (rear)

Failed on 26 first tests4.9 times as often as similar carsPossible evidence

What it means

Chafing, corrosion or damage to a rigid brake pipe justifies rejection once its wall thickness is reduced by a set amount, although DVSA accepts this is not easy to determine. If a tester is not sure, the benefit of the doubt applies. A leaking pipe or connection is graded Dangerous on a hydraulic system and Major on an air system.

Also noted as an advisory

Testers also noted it as an advisory, worn but not yet failing, on 40 first tests, 2.8 times as often as on similar cars.

Data: UK MOT open data, 2025. Compared with cars of the same age and mileage. Advisories count notes recorded on failed first tests only.

Tyres

Two wear patterns. The strongest is the tyre tread depth (rear): 3.0 times as often as on similar cars.

Tyre tread depth (rear)

Failed on 28 first tests3.0 times as often as similar carsWear pattern

What it means

Only primary grooves count when tread depth is assessed: those holding the wear indicators, or cut as deep as those when new. Shallower secondary grooves are ignored. Tread depth below the minimum for the vehicle is Dangerous, and so is a pattern not visible over the whole tread, but that second row applies only to vehicles that need the lower minimum.

Tyre condition (front)

Failed on 40 first tests2.1 times as often as similar carsWear pattern

What it means

Exposed or damaged ply or cords are graded Dangerous. A cut in excess of the requirements and deep enough to reach the ply or cords is Major, and testers may open the cut with a blunt instrument to check its depth. A tyre contacting the vehicle through flexing or suspension movement is not a defect; fouling fails only at the time of test.

Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.

Suspension

Two faults. The strongest is the suspension arm ball joint (front): 2.6 times as often as on similar cars.

Suspension arm ball joint (front)

Failed on 57 first tests2.6 times as often as similar carsPossible evidence

What it means

A suspension arm ball joint is failed under the general suspension pin, bush or joint wording. Excessively worn is Major, and likely to become detached is graded Dangerous.

Also noted as an advisory

Testers also noted it as an advisory, worn but not yet failing, on 27 first tests, 3.4 times as often as on similar cars.

Coil spring (rear)

Failed on 25 first tests2.1 times as often as similar carsPossible evidence

What it means

A missing bump stop rubber is not a reason to fail a coil spring. When the vehicle is jacked and lowered, a spring that does not correctly locate as the suspension returns to its normal running position is rejected as insecurely attached. A missing spring is Major, and graded Dangerous where directional control is affected.

Data: UK MOT open data, 2025. Compared with cars of the same age and mileage. Advisories count notes recorded on failed first tests only.

Advisories

Other things testers noted as worn or close to failing, more often than on similar cars.

An advisory is a note from the tester about something that has not failed yet. It is an early warning, not a fail. Advisories for the faults above are shown with those faults.

Wheel bearings (front)

Noted on 34 first tests10 times as often as similar carsElevated evidence

Rigid brake pipes (front)

Noted on 33 first tests3.9 times as often as similar carsElevated evidence

Exhaust system (rear)

Noted on 29 first tests3.5 times as often as similar carsElevated evidence

Non-component advisories (front)

Noted on 21 first tests2.6 times as often as similar carsElevated evidence

Brake pads (rear)

Noted on 25 first tests2.1 times as often as similar carsWear pattern

Data: UK MOT open data, 2025. Counts cover advisories recorded on failed first tests only, compared with cars of the same age and mileage.

MOT pass rates

How first tests ended, and how the pass rates are counted.

Passed first time
66in every 100
Passed on the first test.
Fixed at the station
5in every 100
Failed, then fixed at the test station the same day.
Failed
29in every 100
Did not pass, and were not fixed at the test station.

First-attempt pass 66.3% of 895 first tests (2025): only cars that passed first time count. Official-style pass 70.9%: cars fixed at the test station also count as a pass. The 5 fixed and the 29 not fixed make the 34 in every 100 that did not pass first time.

Same model, other years

Passed first time in every 100, all tested in 2025.

406080100200520092015Older carsNewer cars
4060801002009Newer cars

Newer cars are younger, so look for a jump rather than the climb. A year earlier (2024), when these cars were a year younger, 63 in every 100 passed first time.

YearPassed first timeFirst tests
200571 in every 100799
200670 in every 1001,098
200767 in every 1001,373
200869 in every 1001,128
2009 This car66 in every 100895
201065 in every 100927
201173 in every 1001,026
201274 in every 1001,012
201371 in every 1002,809
201474 in every 1001,644
201578 in every 1002,729
201679 in every 1002,000
201780 in every 1001,415
201883 in every 100900
201982 in every 1001,002

FAQs

Short answers about how to read this model-year guide.

With 895 first tests, there are too few to say whether the 2009 Mercedes-Benz CLS differs from the model years either side. Its main cause of failure was Suspension arm ball joint (front), about 19 in every 100 failed tests. In 2025, 66.3% of 895 first MOTs on the 2009 Mercedes-Benz CLS passed first time (PRS: items fixed at the station the same day, counted as a fail). The official-style rate including PRS is 70.9%. Among 302 failed first-attempt MOT tests (test year 2025), Rigid brake pipes (rear) appears more often than on similar cars (8.6% of those tests; 26 observed failures; about 4.9× more often than similar cars). There is no single reliability score here; this is a pre-purchase checklist built from DVSA open data, not a guarantee for any individual car.
Ranked by how often they were actually recorded, the items that most often failed a 2009 Mercedes-Benz CLS at the first attempt were Suspension arm ball joint (front) (18.9%), each as a share of the year's failed first attempts. That is what goes wrong most often on the car. The common faults table shows a different measure: faults that are unusual compared with similar cars.
Among failed first-attempt tests we highlight patterns that appear more often than on similar cars. Top example: Rigid brake pipes (rear) (8.6% of those tests; 26 observed failures; about 4.9× more often than similar cars). These are statistical signals, not a diagnosis of any individual car.
Rigid brake pipes (rear) shows up more often than on similar cars (8.6% of those tests; 26 observed failures; about 4.9× more often than similar cars). That does not prove a design fault. Age, mileage, and how the car was used still matter. Treat it as a pre-purchase checkpoint, not a manufacturer service bulletin.
Common MOT problem areas for the 2009 Mercedes-Benz CLS include Rigid brake pipes (rear), Suspension arm ball joint (front), Coil spring (rear). These are the faults that stand out compared with similar cars, not a complete list of what can go wrong on any individual car.
Advisories flag issues noted at the test and are not a fail rate. We show advisory patterns that appear more often than on similar cars among failed first-attempt tests, separate from common failure rows. Use them as early-warning checks, not as a pass/fail score.
This page highlights MOT failure patterns for the 2009 Mercedes-Benz CLS (registration year) using UK DVSA open data for the selected test year. Patterns are compared with cars of a similar age and mileage. It is a buyer checklist from MOT defect statistics, not a full service history or manufacturer service-bulletin list.
No. MOT tests do not cover engine internals, gearboxes, or many electronic modules. Patterns here come from MOT defect statistics only and should not be read as engine or gearbox reliability scores.

About this data

How this page is built and what it can (and can't) say.

These figures come from UK MOT open data for this model year. We surface common failure patterns against similar cars, not a full reliability score, and not a pass/fail verdict on any individual vehicle.

2024 2025

What we include

UK Class 4 cars only. Normal MOT tests (not retests); first test per vehicle per calendar year; results pass, PRS, or fail.

Same-day repairs

PRS means the car failed items that were fixed at the test station and then passed the same day. We count PRS as a first-attempt fail in headline rates so same-day repairs do not hide problems.

How we compare

We compare this model year with other Class 4 cars of similar age and mileage in the same test year. This model family is left out of the peer group so the car is not measured against itself.

What this does not cover

  • MOTs do not cover engine internals, gearboxes, or many electronics; this is not a full reliability score.
  • Common faults come from MOT defect stats, not manufacturer TSBs or recalls.
  • Age and mileage matching reduces, but does not remove, differences in how cars were used and maintained.
  • If the data for a car is too thin to say anything useful, we say so rather than guess.

Contains public sector information licensed under the Open Government Licence v3.0.

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