How reliable is the Mercedes-Benz 300 compared with other cars?

We do not publish a comparison for the Mercedes-Benz 300, because the cars of this model that have been tested do not cover a wide enough range of ages and mileages. Its raw pass rate is 78.2% across 2,635 tests, but comparing a raw rate between models mostly ranks them by how new they are rather than how good they are. The failure and advisory patterns further down the page are still drawn from real tests and are worth reading.

What do testers most often warn about on a Mercedes-Benz 300?

The most common advisory is "Brake pipe damaged or excessively corroded", noted on 16.4% of all Mercedes-Benz 300 tests. An advisory is not a failure: it flags something that will likely need attention before the next test.

What mileage does a Mercedes-Benz 300 usually have at its MOT?

The average odometer reading recorded at test is 112,469 miles. This is the mileage across all tested examples of every age, not an annual figure, so treat it as a description of the fleet rather than a target for one car.

Are most Mercedes-Benz 300 models petrol or diesel?

Of the Mercedes-Benz 300 cars tested, 82% are petrol, 17% are diesel. Fuel type affects which items tend to fail, particularly emissions and exhaust components.

Model reliability file

Mercedes-Benz 300 MOT pass rate & common failures

From 2,635 recorded MOT tests of the Mercedes-Benz 300, published by DVSA.

Data updated 29 July 2026

Quick answer

Across 2,635 MOT tests, 78.2% of Mercedes-Benz 300 tests ended in a pass. This figure is not adjusted for age or mileage, so it is not a reliability ranking: the Mercedes-Benz 300 fleet does not yet cover a wide enough spread of ages and distances to compare it fairly against other models. Its most commonly recorded failure is 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, which appears in 12.5% of failed tests. Cars of this model average 112,469 miles on the odometer when tested.

At a glance

Recorded pass rate

78.2%unadjusted, not comparable2,635 tests

We are not publishing a ranking for the 300. The examples tested do not cover a wide enough spread of ages and mileages to compare it fairly, and an unadjusted pass rate mostly sorts models by how recently they were bought rather than how well they were built. The failure and advisory patterns below come from the same 2,635 tests and are worth reading on their own terms.

DVSA recorded wording

Most common failure items

Share of failed Mercedes-Benz 300 tests in which each item was recorded. One failed test often lists several items, so these do not sum to 100%.

1.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 repaired12.5%
60 occurrencesSuspension mounting corroded or insecure explained
2.A suspension joint dust cover missing or no longer prevents the ingress of dirt etc12.3%
59 occurrencesSuspension joint dust cover missing or split explained
3.The aim of a headlamp is not within limits laid down in the requirements10.0%
48 occurrencesHeadlamp aim incorrect explained
4.A lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning8.5%
41 occurrencesLamp not working explained
5.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 functioning8.3%
40 occurrencesLamp not working explained
6.Emissions levels exceed default limits7.7%
37 occurrencesEmissions above the permitted limit explained
7.Wiper blade missing or obviously not clearing the windscreen7.1%
34 occurrencesWiper or washer not working properly explained
8.Windscreen washers not working or not providing sufficient fluid to clear the windscreen6.9%
33 occurrencesWiper or washer not working properly explained
9.Brake pipe damaged or excessively corroded6.7%
32 occurrencesBrake pipe corroded explained
10.Significant brake effort recorded with no brake applied indicating a binding brake6.0%
29 occurrencesBrake binding or imbalanced across an axle explained

Warnings without a failure

Most common advisories

Share of all Mercedes-Benz 300 tests carrying each advisory. The denominator differs from the failure list above because an advisory can be issued on a car that passed.

1.Brake pipe damaged or excessively corroded16.4%
431 testsBrake pipe corroded explained
2.Fluid leaking excessively and likely to harm the environment or to pose a safety risk to other road users14.6%
384 tests
3.A tyre seriously damaged12.3%
324 testsTyre damaged or deteriorated explained
4.A spring or spring component fractured or seriously weakened12.3%
323 testsRoad spring broken or fractured explained
5.A wheel bearing with excessive play6.1%
160 testsWheel bearing has excessive play or is rough explained
6.Tyre tread depth not in accordance with the requirements5.9%
156 testsTyre worn close to the legal limit explained
7.Exhaust system leaking or insecure4.8%
127 testsExhaust leaking or insecure explained
8.Brake disc or drum excessively weakened, insecure or fractured4.4%
115 testsBrake disc worn, pitted or scored explained

What gets tested

The 300 fleet

Average mileage recorded at test: 112,469
Fuel mix of tested cars: Petrol82.5%
Diesel17.0%

Trim names grouped into this model (3)

Recorded exactly as DVSA holds them. Trim-level names are rolled up so one model is not split across a dozen thin pages.

300 D
300 S
300 SL

Check a specific Mercedes-Benz 300

A model average tells you the pattern. Its own MOT record tells you the car.

Compare within the range

Other Mercedes-Benz models

Mercedes-Benz A-Class — 73.3% adjusted
Mercedes-Benz C-Class — 77.0% adjusted
Mercedes-Benz E-Class — 78.5% adjusted
Mercedes-Benz GLA — 82.3% adjusted
Mercedes-Benz Vito — 71.0% adjusted
Mercedes-Benz GLC — 85.9% adjusted
All Mercedes-Benz models

Common questions

How reliable is the Mercedes-Benz 300 compared with other cars?: We do not publish a comparison for the Mercedes-Benz 300, because the cars of this model that have been tested do not cover a wide enough range of ages and mileages. Its raw pass rate is 78.2% across 2,635 tests, but comparing a raw rate between models mostly ranks them by how new they are rather than how good they are. The failure and advisory patterns further down the page are still drawn from real tests and are worth reading.
What is the most common MOT failure on a Mercedes-Benz 300?: The item recorded most often is "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", which appears in 12.5% of failed Mercedes-Benz 300 tests. Because one failed test can list several items, these shares do not add up to 100%.
What do testers most often warn about on a Mercedes-Benz 300?: The most common advisory is "Brake pipe damaged or excessively corroded", noted on 16.4% of all Mercedes-Benz 300 tests. An advisory is not a failure: it flags something that will likely need attention before the next test.
What mileage does a Mercedes-Benz 300 usually have at its MOT?: The average odometer reading recorded at test is 112,469 miles. This is the mileage across all tested examples of every age, not an annual figure, so treat it as a description of the fleet rather than a target for one car.
Are most Mercedes-Benz 300 models petrol or diesel?: Of the Mercedes-Benz 300 cars tested, 82% are petrol, 17% are diesel. Fuel type affects which items tend to fail, particularly emissions and exhaust components.

How this was worked out

Method and limits

Figures come from the DVSA anonymised MOT testing dataset, published under the Open Government Licence. Only class 4 initial tests are counted: retests are excluded so a car appears once, and abandoned tests are excluded entirely. No adjusted rate is shown because this model's tested examples do not cover enough of the national age and mileage range for standardisation to mean anything.

An MOT measures whether a car met a legal standard on the day. It is not a breakdown record, a service history or a running-cost estimate, and a pass rate is a property of a fleet rather than a prediction about one car.