Performance by cohort

3 year bands · 776,502 tests

Pass rate climbs 11.7 points across the cohorts — newer C examples clear the test more reliably than the early cars.

Pre-2018 cohort 668,375

Pass

79.0%

Fail

16.9%

PRS

3.4%

Avg mileage at test

92,918 mi

2018–2020 cohort 104,345

Pass

89.5%

Fail

8.4%

PRS

1.6%

Avg mileage at test

42,558 mi

2021+ cohort 3,782

Pass

90.7%

Fail

7.5%

PRS

1.6%

Avg mileage at test

27,147 mi

Cohort = vehicle's first-registration year band. Same model, different generations of build.

The picture

C-Class Passes 78% But Costs More When It Fails

A 78.1% pass rate from 461,751 tests puts the C-Class ahead of most rivals in its segment. Pre-facelift models are where trouble concentrates: quality complaints are widespread, and owners of the C220 CDI automatic have flagged a disappointing gearbox from new. Suspension bushes and worn tyres are the most common failure triggers; at an average test mileage of 84,016, tread depth problems are often deferred maintenance rather than sudden wear.

Repair bills are steep. An electric steering rack failure on a 2016 car came to £2,200 for a reconditioned unit. The 220 diesel also attracted a 9 mpg economy drop after a voluntary emissions update. A pre-purchase check from an independent Mercedes specialist is money well spent.

ABI Insurance Group

Group 28–44

A high-group car — insurance costs will be significantly above average. Lower groups cost less to insure; UK fleet average is around Group 22.

Source: ABI Group Rating Panel · administered by Thatcham Research · groups cover standard variants; performance trims may sit higher. Browse all insurance groups →

28–44

out of 50

Compare quotes →

Top ten reasons for rejection.

Filter failures:

Hide wear items to see the model's real defects.

01

A suspension pin, bush or joint excessively worn

22,646 occurrences · 2.9% of tests
02

Tyre tread depth not in accordance with the requirements

19,692 occurrences · 2.5% of tests
03

Windscreen or window damaged or seriously discoloured but not adversely affecting driver's view

18,504 occurrences · 2.4% of tests
04

A spring or spring component fractured or seriously weakened

13,169 occurrences · 1.7% of tests
05

A suspension joint dust cover severely deteriorated

12,922 occurrences · 1.7% of tests
06

Brake pipe damaged or excessively corroded

10,232 occurrences · 1.3% of tests
07

A tyre cords visible or damaged

9,555 occurrences · 1.2% of tests
08

A suspension joint dust cover missing or no longer prevents the ingress of dirt etc

7,788 occurrences · 1.0% of tests
09

A tyre seriously damaged

7,559 occurrences · 1.0% of tests
10

A suspension joint dust cover severely deteriorated

7,022 occurrences · 0.9% of tests

Counts cover Major and Dangerous defects logged at test. Advisory items excluded so this shows why a car was rejected, not just what the tester flagged in passing.

Worst-case fix budget · top 4 failures

£300–£815

If every one of this C's most-logged Major fails hit at the same MOT, that's the real-world UK garage range. Reality is usually one or two items, not all of them. Open the estimator →

Try the calculator

Build your own retest budget.

Year-band analysis

Best year to buy. Worst to avoid.

First-time MOT pass rate split by registration band. A 11.7-point gap between bands means the year you buy Mercedes Benz C has a real effect on what turns up at the garage.

Best band to buy

90.7%

2021+ registration

the 2021-on band climbs to 90.7% — a 11.7-point improvement. Tests in this band average 27,147 miles — roughly 66K miles fewer on the clock than the older band. Failures here are mostly wear items: has a cut in excess of the…, tread depth below requirements of 1.6mm — the structural issues that drag down older examples don't appear in the top-10 for this band. Post-2020 examples are early in their MOT life and generally show the cleanest records.

Band to be cautious about

79.0%

Pre-2018 registration

On the older band (pre-2018), the data shows a 79.0% pass rate against a fleet average of 90.7% on the newer band. The main culprits logged at test: ball joint excessively worn, tread depth below requirements of 1.6mm, and damaged but not adversely affecting driver's view. Average mileage on test for this band is 92,918 miles — high-mileage wear items are a recurring theme. Honest John records: "High speed vibration reported from C350e, particularly noticeable on smooth motorways. Owner has chenged tyres and has a 4-way laser alignment to no avail. MB dealer puzzled. No problem with…"

Best band to buy: 2021+ (90.7% first-time pass). Worst band to avoid: pre-2018 (79.0% pass). That's a 11.7-point spread across 668,375 older tests and 3,782 newer ones — year of build makes a material difference on this model.

Year-spread leaderboard →

Tools that pre-empt a retest.

Picked against this car's top failure patterns. Affiliate links to Amazon UK — we earn a small cut at no cost to you. Disclosed up-front, doesn't shape the data.

Item 01 · Amazon UK

Digital tyre-tread depth gauge

Five quid for a gauge beats £150 for a retest. UK MOT minimum is 1.6mm — most testers fail anything below 2mm to be safe.

Search Amazon UK

My Motor World · affiliate

Parts & supplies for this fix

Affiliate links — small commission, no extra cost to you.

Denso

Denso W14E Spark Plug (Single)

£1.09

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Denso

Denso W16EX-U Spark Plug (Single)

£1.09

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Denso

Denso W16FSR Spark Plug (Single)

£1.09

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Denso

Denso W9LM-US Spark Plug (Single)

£1.09

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Click Mechanic · affiliate

Book a mobile mechanic

Affiliate links — small commission, no extra cost to you.

Mobile mechanic · UK-wide

Book a mechanic at your door.

Fixed-price quotes upfront. No garage needed. Click Mechanic sends a vetted local mechanic to you — home, work, or roadside.

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Owner reports · Honest John

What owners actually report.

Verbatim faults logged by owners on honestjohn.co.uk over recent years. We didn't summarise — these are the words people typed in.

What's good

Much improved interior quality. More refined and better to drive than predecessor. Strong 2.0-litre four-cylinder diesel engines on facelifted cars.

Where it falls short

C220 CDI with automatic gearbox is disappointing. Surprising quality issues with pre-facelift models.

Recent owner-reported faults

19 Oct 2020
Report of electric steering motor failure on 2016 C-Class. Dealer recommends replacing the full steering rack as the motor is part of the component. £2200 for reconditioned unit fitted. Mercedes-Benz UK has offered to cover 50 per cent of the repair cost.
23 Feb 2020
Owner of 220 diesel reports a 9mpg drop in fuel economy after voluntary dealer emissions update.
20 Jan 2020
Further report of front wheels of April 2019 Mercedes Benz C43 AMG "skipping badly when manoeuvring at very low speed resulting in a disconcertingly loud noise akin to having collided with a kerb."
3 Jan 2020
Report of failure of the brakes of 2105 Mercedes Benz C300 D BlueTec hybrid at 88,000 miles. The servo assistance vacuum pump had failed. Needed attention by MB dealer because MB independent not qualified to work on a hybrid. Marshall Care Plan B warranty taken out when car was bought not pay out as it's not a listed part.
17 Dec 2019
Report of rattle from engine of Mercedes-Benz C200 EQ Boost (48v mild hybrid) purchased in May 2019. Within a couple of weeks owner reported a "serious engine rattle" to the supplying Mercedes dealer who said there was nothing wrong with. He then got management involved and they changed a pulley, belt and tensioner, but it made no difference. They then got their group technician involved. He submitted his findings to Mercedes-Benz and they fitted a redesigned crank pulley, but again the noise did not improve so owner served a rejection letter on the dealership and they submitted an exchange vehicle application, but Mercedes said there’s nothing wrong with the car as they have been able to reproduce the noise in some of the other C200 EQ Boosts and they can do some things to reduce the noise.
24 Nov 2019
Report of transmission failure of 2005/65 Mercedes Benz W205 C220 automatic at 35,000 miles; car correctly serviced on time by the MB dealer. Part to repair quoted at £1200 + labour (total of £1,644). MB is not initially offering any help towards cost from a goodwill view point. Car is 8 months out of manufacturer warranty, but owner may have Sale of Goods case law rights.
15 Nov 2019
Report that after the NOx emissions software update a Mercedes-Benz C250d 4matic will not shift up from 8th to 9th gear until 75mph (previously 68mph). 9th can be selected on the paddles, but box shifts back down to 8th at about 65mph.
25 Oct 2019
Report of front wheels of Mercedes-Benz C43 4-Matic 'skipping'.
9 Sep 2019
Report of smell of petrol outside February 2015 Mercedes Benz C200 Sport auto. Will be a blocked charcoal filter in the fuel tank breather system.
4 May 2019
Petrol smell reported from March 2016 Mercedes Benz W205 C200 only just out of warranty. Car had its last service with Mercedes in the middle of March. Owner reported to dealer in April 2019 and dealer had the cheek to inform him there would be a £165 'diagnosis fee' to establish the cause of what is actually a very well known problem of the carbon filter in the fuel tank breathing system becoming blocked. Shoud be fixed FoC. Same thing happens on A-Class.
22 Apr 2019
Complaint of 2017 Mercedes-Benz C43 AMG 4-Matic clunking its front tyres on full lock. 4,000 miles from new. Been back to the local Mercedes dealer for investigation under warranty but returned in same the same condition. There are two cures. One is different tyres. But the correct cure is a replacement steering knuckle joint that is correctly engineered for RHD cars.
21 Oct 2018
High speed vibration reported from C350e, particularly noticeable on smooth motorways. Owner has chenged tyres and has a 4-way laser alignment to no avail. MB dealer puzzled. No problem with Airmatic suspension. Seems to be driveline.

Source: honestjohn.co.uk · 30 reports indexed, top 12 shown

Buying or keeping a C?

Use the failure ranking as a pre-test checklist or a haggling lever. Treat the headline pass rate as a fleet-wide trend, not a guarantee on any individual car.

If you own a C and your last MOT looked nothing like the ranked failures above, that's normal — individual cars vary widely. The ranking shows the patterns testers flag most often across the country.