MOT cost .

Mercedes Benz

300

3,384 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 1.7 points above the UK fleet average across our 1,988 tracked models — a confident result.

Pass

77.5%

Pass-after-fix

3.5%

Fail

17.6%

Avg miles

114,799

Pass + Pass-after-fix + Fail = 100%

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.

Top ten reasons for rejection.

  1. 01

    A suspension joint dust cover severely deteriorated

    206 occurrences · 6.1% of tests

  2. 02

    Steering rack gaiter or ball joint dust cover damaged or deteriorated

    87 occurrences · 2.6% of tests

  3. 03

    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

    79 occurrences · 2.3% of tests

  4. 04

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

    73 occurrences · 2.2% of tests

  5. 05

    A lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning

    71 occurrences · 2.1% of tests

  6. 06

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

    66 occurrences · 2.0% of tests

  7. 07

    The aim of a headlamp is not within limits laid down in the requirements

    57 occurrences · 1.7% of tests

  8. 08

    Wiper blade missing or obviously not clearing the windscreen

    51 occurrences · 1.5% of tests

  9. 09

    An obligatory rear fog lamp missing, or a front or rear fog lamp inoperative or in the case of a multiple light source more than 1/2 not functioning

    51 occurrences · 1.5% of tests

  10. 10

    Brake pipe damaged or excessively corroded

    49 occurrences · 1.4% 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 2 failures

£160–£480

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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Build your own retest budget.

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.