Mercedes-Benz 300 MOT pass rate & common failures
The Mercedes-Benz 300 appears in 17,003 MOT tests spanning model years 1980–2022, and 82.6% of them passed. All cars of a similar age fail 21.7% of the time, so this is 4.3pp better than the group it competes with. Its most common failure areas are lighting & signalling, suspension and brakes.
Best and worst 300 years
Ranked across 300 years with at least 1,000 tests. Older cars fail more simply because they are older — compare years close together in age before drawing conclusions.
What the MOT record shows
Build year matters more than the headline suggests: 1989 cars pass 85.0% of the time while 1993 cars manage 80.7%, a 4.3-point spread.
Lighting & signalling dominates the failure mix at 10.6% of all tests — 4.3 points clear of suspension, so it is the first thing to check.
At component level the recurring items are headlamp aim, service brake performance and position lamp — headlamp aim alone was recorded 809 times.
Condition tracks the odometer closely. Failures run at 13.9% in the 0-30k band and 22.4% in the 150k+ band, a 8.5-point spread.
Split by fuel, diesel examples fail 5.7pp more often than petrol ones (22.0% vs 16.3%) — worth weighing if you have a choice.
Advisories point at the next bill rather than this one: suspension was flagged on 23.4% of tests without failing them.
The trend is improving — the fail rate fell from 18.9% in 2021 to 16.2% in 2025, as the worst-kept examples leave the fleet.
How it compares
By model year
Every 300 model year with a usable sample. Years with their own detailed report are linked.
| Year | Tests | Pass rate | Fail rate | Most common failure |
|---|---|---|---|---|
| 1982 | 72 | 83.3% | 16.7% | Lighting & signalling |
| 1983 | 93 | 76.3% | 23.7% | Lighting & signalling |
| 1984 | 129 | 81.4% | 18.6% | Lighting & signalling |
| 1985 | 149 | 75.8% | 24.2% | Lighting & signalling |
| 1986 | 973 | 81.7% | 18.3% | Lighting & signalling |
| 1987 | 1,606 | 84.6% | 15.4% | Lighting & signalling |
| 1988 | 2,267 | 82.5% | 17.5% | Lighting & signalling |
| 1989 | 3,084 | 85.0% | 15.0% | Lighting & signalling |
| 1990 | 1,859 | 81.7% | 18.3% | Lighting & signalling |
| 1991 | 2,333 | 81.2% | 18.8% | Lighting & signalling |
| 1992 | 2,371 | 82.7% | 17.3% | Lighting & signalling |
| 1993 | 1,271 | 80.7% | 19.3% | Lighting & signalling |
| 1994 | 171 | 74.9% | 25.1% | Lighting & signalling |
| 1995 | 33 | 84.9% | 15.2% | Visibility |
| 1996 | 31 | 90.3% | 9.7% | Lighting & signalling |
| 1997 | 36 | 88.9% | 11.1% | Lighting & signalling |
| 1998 | 33 | 81.8% | 18.2% | Lighting & signalling |
| 1999 | 46 | 76.1% | 23.9% | Lighting & signalling |
| 2009 | 38 | 86.8% | 13.2% | Lighting & signalling |
| 2010 | 40 | 75.0% | 25.0% | Brakes |
| 2011 | 37 | 70.3% | 29.7% | Lighting & signalling |
Most common failures (all years)
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 10.6% | 1,795 |
| 2 | Suspension | 6.3% | 1,073 |
| 3 | Brakes | 6.3% | 1,071 |
| 4 | Body, structure & corrosion | 4.8% | 813 |
| 5 | Visibility | 4.2% | 720 |
| 6 | Emissions & environmental | 3.2% | 547 |
| 7 | Steering | 1.9% | 328 |
| 8 | Tyres | 1.9% | 322 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Headlamp aim | 809 |
| 2 | Service brake performance | 502 |
| 3 | Position lamp | 465 |
| 4 | Component mounting prescribed areas | 454 |
| 5 | Washers | 424 |
| 6 | Wipers | 406 |
| 7 | Ball joint dust cover | 380 |
| 8 | Headlamp | 335 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Suspension | 23.4% | 3,977 |
| 2 | Brakes | 21.8% | 3,706 |
| 3 | Emissions & environmental | 16.7% | 2,846 |
| 4 | Tyres | 12.6% | 2,144 |
| 5 | Body, structure & corrosion | 10.8% | 1,835 |
| 6 | Steering | 9.1% | 1,554 |
Failure rate by mileage
Higher-mileage cars tend to fail more — often the most useful guide to real condition.
| Mileage band | Tests | Fail rate |
|---|---|---|
| 0-30k | 707 | 13.9% |
| 30-60k | 2,033 | 12.2% |
| 60-90k | 3,416 | 14.5% |
| 90-120k | 3,711 | 17.1% |
| 120-150k | 2,955 | 18.6% |
| 150k+ | 4,171 | 22.4% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Petrol | 13,582 | 16.3% |
| Diesel | 3,412 | 22.0% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 3,998 | 18.9% |
| 2022 | 3,578 | 16.6% |
| 2023 | 3,329 | 17.9% |
| 2024 | 3,135 | 17.0% |
| 2025 | 2,963 | 16.2% |
What to check before buying a Mercedes-Benz 300
- Lighting & signalling (10.6% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Suspension (6.3% of tests): Worn drop links, bushes, springs or shocks — listen for knocks over bumps and check for uneven tyre wear. Typical repair: £150–£450 per corner.
- Brakes (6.3% of tests): Pads/discs are routine wear; binding, imbalance or corroded pipes are more serious — test for pulling under braking. Typical repair: £100–£350 per axle.
Repair costs are rough UK ballpark ranges to set expectations, not quotes — actual prices vary widely by car, parts and garage.
Frequently asked questions
What is the MOT pass rate for the Mercedes-Benz 300?
82.6% of the 17,003 Mercedes-Benz 300 MOT tests in this dataset passed, a 17.4% fail rate, across model years 1980–2022.
What does the Mercedes-Benz 300 most often fail its MOT on?
Lighting & signalling, recorded in 10.6% of tests, then suspension (6.3%).
Which 300 years are best and worst for MOT results?
1989 has the best pass rate at 85.0% and 1993 the weakest at 80.7%, from 3,084 and 1,271 tests respectively.
How much does mileage affect 300 MOT results?
Fail rates run at 13.9% for cars in the 0-30k band and 22.4% for 150k+, a 8.5-point difference.
Is the petrol or diesel 300 more reliable at MOT time?
On MOT-testable defects the petrol fails 16.3% of the time against 22.0% for the diesel. This covers testable items only, not engine or gearbox reliability.
Methodology & source. Based on 17,003 MOT tests. Dataset: DVSA MOT testing data (2021,2022,2023,2024,2025). Data last updated 2026-07-27. Figures reflect MOT-testable defects only — read the methodology for how these are calculated and what they don't measure.