Mercedes Benz
300
8,568 MOT tests analysed. lands in the middle of the pack — here's where 300s pass, fail, and end up on the retest sheet.
That's 1.1 points above the UK fleet average across our 1,984 tracked models — a confident result.
Pass
78.6%
Pass-after-fix
3.9%
Fail
16.4%
Avg miles
115,123
Pass + Pass-after-fix + Fail = 100%
This model's production run straddles the January 2006 Euro 4 cutoff. Individual cars vary — check your registration plate on the government's ULEZ checker. Daily charges if driven in the zone: London £12.50 · Birmingham £8.00 .
The picture
300: middle-of-the-pack on first-time pass
Across 3,384 MOT tests, the 300 returns 77.5% first-time pass — roughly in line with the UK fleet average. The single most-logged Major fail is a torn suspension dust cover. A torn steering gaiter and the strength or continuity of the load bearing round out the top three. Average tested mileage sits at 114,799, which is the lens to read those failure rankings through. If you own one and the next test is close, the ranked list below is a sensible pre-test checklist.
ABI Insurance Group
Group 28–46
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 →
28–46
out of 50
Top ten reasons for rejection.
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- 01
A suspension joint dust cover severely deteriorated
390 occurrences · 4.6% of tests
- 02
Steering rack gaiter or ball joint dust cover damaged or deteriorated
181 occurrences · 2.1% of tests
- 03
Windscreen or window damaged or seriously discoloured but not adversely affecting driver's view
176 occurrences · 2.1% of tests
- 04
A lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning
123 occurrences · 1.4% of tests
- 05
The aim of a headlamp is not within limits laid down in the requirements
116 occurrences · 1.4% of tests
- 06
A suspension joint dust cover missing or no longer prevents the ingress of dirt etc
113 occurrences · 1.3% of tests
- 07
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
109 occurrences · 1.3% of tests
- 08
A rear registration plate lamp or light source missing or inoperative in the case of multiple lamps or light sources
103 occurrences · 1.2% of tests
- 09
Emissions levels exceed default limits
101 occurrences · 1.2% of tests
- 10
Wiper blade missing or obviously not clearing the windscreen
100 occurrences · 1.2% 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 3 failures
£170–£560
If every one of this 300'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 →
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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.
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Buying or keeping a 300?
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 300 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.