Verdict
The 2015 Mercedes-Benz C-Class 2.1 diesel passes its MOT first time on 81.2% of tests, against 75.5% for a typical car of the same age and mileage. It beats 84% of cars on UK roads.
Its lead grows with age. At its first MOT it is about 3 points ahead of a typical car; by 8 years old it passes about 7 points more often, and by 10–11 years about 8 points more often. Across all years of the 2.1 diesel, it is about level with a typical car under 20,000 miles and about 6–7 points ahead from 60,000 to 120,000 miles.
2014 and 2015 are the best years of this engine, each beating more than eight in ten cars; 2016 cars beat about eight in ten, and 2017 and 2018 cars nearly three in four. Even the weakest years since 2001, 2005 and 2006, beat about six in ten cars for their age. Among 2015 C-Class engines, the 2.0 petrol beats more than nine in ten cars and the 2.1 diesel hybrid nearly nine in ten; the 1.6 diesel beats about three in four. The C-Class as a whole beats about three in four.
Lights, steering, bodywork and brakes fail far less often than on a typical car. The weak spots are suspension ball joints (2.2 times as often as a typical car), the engine warning light (1.9 times), number plates (1.6 times) and tyre tread depth (1.4 times).
Watch these weak spots
MOT pass rate by age
First-time pass rate at each MOT.
Where it fails
Each area compared with a typical car of the same age and mileage, in points of pass rate. Tap or hover an area to see what to check.
Every MOT area
Share of tests failing on each area, against a typical car of the same age and mileage (black line).
Buying one or MOT due? Check these
- Suspension ball joints
The clearest weak spot: they fail on about 1 in 40 tests, 2.2 times as often as on a typical car, and testers advise on them about 5 times as often. Listen for knocks over speed bumps and feel for wandering or vague steering. - Tyre tread depth
The most common fail, on about 1 in 25 tests (1.4 times the typical rate), and an advisory on about one test in five. Check every tyre, including the inner edge, has at least 3 mm of tread. - Engine warning light
Fails about 1.9 times as often as on a typical car, on about 1 in 45 tests. It should come on with the ignition and go out once the engine starts; if it stays on, get the fault codes read before you buy. - Number plates
Rare (about 1 in 230 tests) but 1.6 times the typical rate. Check both plates are secure, legible and not cracked or faded. - Tyre damage
Fails on about 1 in 30 tests, about the same as a typical car. Look for cuts, bulges and cracking on both sidewalls of every tyre. - Coil springs
Fail on about 1 in 55 tests, about as often as on a typical car. Look behind each wheel for a snapped coil and listen for clunks over bumps.
Pass rate by mileage
First-time pass rate by mileage at the test.
Most common MOT failures
| Item | This car | Typical | vs typical |
|---|---|---|---|
| Tyre tread depth | 3.9% | 2.7% | 1.4× |
| Tyre damage & cracking | 3.5% | 3.3% | 1.0× |
| Suspension ball joints | 2.4% | 1.1% | 2.2× |
| Engine warning light | 2.2% | 1.2% | 1.9× |
| Coil springs | 1.8% | 1.8% | 1.0× |
| Brake pads | 1.7% | 2.3% | 0.7× |
| Headlight aim | 1.7% | 2.4% | 0.7× |
| Windscreen washers | 1.0% | 1.8% | 0.6× |
| Tyre pressure warning (TPMS) | 0.6% | 1.0% | 0.7× |
| Windscreen wipers | 0.6% | 2.0% | 0.3× |
Specific defects found
Tester wording for the most frequent failure items, per 1,000 tests.
| Defect | per 1,000 |
|---|---|
| Tyre tread depth not in accordance with the requirements | 38.9 |
| A suspension pin, bush or joint excessively worn | 26.1 |
| Engine MIL illuminated indicating a malfunction | 22.4 |
| A tyre seriously damaged | 18.9 |
| A spring or spring component fractured or seriously weakened | 18.2 |
| The aim of a headlamp is not within limits laid down in the requirements | 16.8 |
| A tyre cords visible or damaged | 15.4 |
| A brake lining or pad worn below 1.5mm | 12.7 |
Pick a make and model to see its MOT pass rate, best and worst years and weak spots.
Advisories
Not a fail yet, but likely to need attention soon.
| Item | Share of tests | vs typical |
|---|---|---|
| Tyre tread depth | 21.1% | 1.2× |
| Brake discs | 9.3% | 1.0× |
| Brake pads | 7.4% | 0.9× |
| Tyre damage & cracking | 4.2% | 0.6× |
| Suspension ball joints | 4.1% | 4.8× |
| Suspension arm bushes | 1.3% | 0.4× |
| Number plates | 1.0% | 0.7× |
| Engine oil leaks | 0.9% | 0.5× |
Best and worst years
C-Class 2.1 Diesel by year, ranked against all cars on UK roads after adjusting for age and mileage. Green = better than half of cars.
Other 2015 C-Class engines
Grades compare each car with cars of the same age and mileage (A = best 20% of cars on UK roads, E = worst 20%), so an older or higher-mileage car can grade above one with a higher pass rate.
| Engine | Pass rate | Rank | Grade |
|---|---|---|---|
| 2.1 Diesel | 81.2% | Beats 84% | A |
| 2.0 Petrol | 85.4% | Beats 93% | A |
| 2.1 Diesel hybrid | 81.3% | Beats 89% | A |
| 1.6 Diesel | 79.7% | Beats 74% | B |
| 1.6 Petrol | 82.1% | Beats 72% | B |
| 4.0 Petrol | 87.5% | Beats 96% | A |
| 2.0 Hybrid | 85.8% | Beats 98% | A |
FAQ
What is the MOT pass rate of a 2015 Mercedes-Benz C-Class 2.1 diesel?
81.2% of MOT tests on the 2015 C-Class 2.1 diesel were passed first time, from 218,090 tests. A typical car of the same age and mileage passes 75.5%.
Is the 2015 Mercedes-Benz C-Class 2.1 diesel reliable?
On MOT results it is well above average: it beats 84% of cars on UK roads, and its lead over a typical car grows as it gets older. MOT results cover safety and emissions items, not every kind of breakdown.
What are the most common MOT failures on the 2015 C-Class 2.1 diesel?
Tyre tread depth (about 1 in 25 tests), tyre damage, suspension ball joints and the engine warning light. Ball joints fail 2.2 times as often as on a typical car.
Which year of C-Class 2.1 diesel is best?
2014 and 2015 cars each beat more than eight in ten cars on UK roads once age and mileage are taken into account, 2016 cars about eight in ten and 2017 and 2018 cars nearly three in four. No year since 2001 is below average.
Which 2015 C-Class engine is best?
The 2.0 petrol beats more than nine in ten cars and the 2.1 diesel hybrid nearly nine in ten, slightly ahead of the 2.1 diesel, while the rarer 4.0 petrol and 2.0 hybrid do even better on far fewer tests. The 1.6 diesel beats about three in four.
Is a high-mileage C-Class 2.1 diesel a good buy?
On MOT results it holds up well: across all years of the 2.1 diesel it passes about 6–7 points more often than a typical car between 60,000 and 120,000 miles. Check the suspension ball joints and the engine warning light.