Mercedes Benz
420
1,775 MOT tests analysed. sits above the UK fleet average — here's where 420s pass, fail, and end up on the retest sheet.
That's 3.7 points above the UK fleet average across our 1,984 tracked models — a confident result.
Pass
81.2%
Pass-after-fix
2.6%
Fail
14.0%
Avg miles
103,122
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
420: above-average pass rates, with caveats
Across 659 MOT tests, the 420 returns 83.0% first-time pass — above the UK fleet average. The single most-logged Major fail is a torn suspension dust cover. Windscreen washers not working and the strength or continuity of the load bearing round out the top three. Average tested mileage sits at 101,734, 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
144 occurrences · 8.1% of tests
- 02
A suspension joint dust cover missing or no longer prevents the ingress of dirt etc
51 occurrences · 2.9% of tests
- 03
The aim of a headlamp is not within limits laid down in the requirements
32 occurrences · 1.8% of tests
- 04
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
30 occurrences · 1.7% of tests
- 05
Wiper blade missing or obviously not clearing the windscreen
28 occurrences · 1.6% of tests
- 06
Windscreen or window damaged or seriously discoloured but not adversely affecting driver's view
25 occurrences · 1.4% of tests
- 07
Significant brake effort recorded with no brake applied indicating a binding brake
25 occurrences · 1.4% of tests
- 08
A rear registration plate lamp or light source missing or inoperative in the case of multiple lamps or light sources
25 occurrences · 1.4% of tests
- 09
Exhaust system leaking or insecure
24 occurrences · 1.4% of tests
- 10
Headlamp reflector or lens slightly defective
21 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 4 failures
£190–£605
If every one of this 420'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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Build your own retest budget.
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
Headlight restoration kit
Yellowed lenses fail the light-output test. A restoration kit lifts the haze in an afternoon for £20.
Search Amazon UK
Item 02 · Amazon UK
Bosch Aerotwin wiper blades
Cheap wipers fail the test on smear streaks. Bosch Aerotwins last a winter and clear a screen properly.
Search Amazon UK
My Motor World · affiliate
Parts & supplies for this fix
Affiliate links — small commission, no extra cost to you.
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.
Buying or keeping a 420?
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 420 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.