Diesel Mercedes-Benz 300: MOT pass rate

76.1% of diesel Mercedes-Benz 300s pass the MOT first time, measured across 522 DVSA tests on that fuel type alone. Average mileage at test was 147,671.

Diesel against the other Mercedes-Benz 300 versions

Why the fuel type changes the number

Diesels carry DPFs, EGR valves and stricter smoke limits, so emissions and exhaust faults account for failures petrol cars never see.

On the Mercedes-Benz 300 specifically, petrol is the strongest at 81.9%, and this diesel version sits 4.8 points below the 80.9% model average.

What it means if you are buying one

The diesel Mercedes-Benz 300 fails more often than the model average, so budget for the items that catch this fuel type and treat a fresh MOT as worth paying for. Buying a damaged one? run it through the analyzer, check the exact car, decode the VIN and check the mileage before you bid.

Mileage is part of the answer

The average diesel Mercedes-Benz 300 had covered 147,671 miles at test, against 107,424 for the petrol. That is very high mileage. Clutches, dual-mass flywheels and head gaskets have usually been through at least one repair by this point, so ask for evidence rather than assume the car is original everywhere.

Fuel type and mileage are tangled together: diesels are usually bought by higher-mileage drivers, so some of any gap between fuels is the miles rather than the engine. The per-year figures on the Mercedes-Benz 300 page separate age from fuel if you want to isolate one.

Most common MOT failures on a diesel Mercedes-Benz 300

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 repaired, 5.8% of tests (6.19x the national rate for this defect)
2. Steering rack gaiter or ball joint dust cover missing or no longer prevents the ingress of dirt etc, 3.6% of tests (4.82x the national rate for this defect)
3. Exhaust system leaking or insecure, 3.4% of tests (3.35x the national rate for this defect)
4. Significant brake effort recorded with no brake applied indicating a binding brake, 3% of tests (2.91x the national rate for this defect)
5. The aim of a headlamp is not within limits laid down in the requirements, 4% of tests (1.69x the national rate for this defect)
6. Windscreen washers not working or not providing sufficient fluid to clear the windscreen, 2.6% of tests (1.57x the national rate for this defect)
7. A lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning, 2.6% of tests (1.19x the national rate for this defect)
8. 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, 2.5% of tests (5.58x the national rate for this defect)
9. A suspension pin, bush or joint excessively worn, 2.5% of tests
10. A spring or spring component fractured or seriously weakened, 2.3% of tests

From 530 DVSA-tracked diesel Mercedes-Benz 300 tests, 2024, split out from the Mercedes-Benz 300's other fuel types. DVSA testers marked 4.32% of these flagged defects as "dangerous", against 5.11% nationally. See which fuel type fails on the most dangerous defects nationally for how that compares across the whole fleet.

Most common MOT advisories on a diesel Mercedes-Benz 300

Flagged but doesn't fail the car, a different list from the failures above.

1. A wheel bearing with excessive play, 14.3% of tests (22.1x the national rate for this defect)
2. A flexible brake hose excessively damaged, deteriorated, chafed, twisted or stretched, 8.1% of tests (14.48x the national rate for this defect)
3. 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, 7.4% of tests (4.85x the national rate for this defect), also fails
4. Vehicle structure corroded to the extent that the rigidity of the assembly is seriously reduced, 5.7% of tests (4.55x the national rate for this defect)
5. Brake pipe damaged or excessively corroded, 28.1% of tests (4.54x the national rate for this defect)
6. A steering ball joint with excessive wear or free play, 6% of tests (4.53x the national rate for this defect)
7. A brake hose ferrule excessively corroded, 5.1% of tests (4x the national rate for this defect)
8. Exhaust system leaking or insecure, 8.1% of tests (2.85x the national rate for this defect), also fails
9. Fluid leaking excessively and likely to harm the environment or to pose a safety risk to other road users, 15.1% of tests (2.71x the national rate for this defect)
10. A spring or spring component fractured or seriously weakened, 10.6% of tests (2.24x the national rate for this defect), also fails

From 530 DVSA-tracked diesel Mercedes-Benz 300 tests, 2024.

Other Mercedes-Benz 300 fuel types

• Petrol Mercedes-Benz 300 - 81.9%

All Mercedes-Benz 300 MOT data · Every model