Audi A3 vs Mercedes A Class
Take the Audi A3 for lower age-adjusted MOT risk: its index is 82.1 versus 91.3 for the Mercedes A Class, and the 95% confidence intervals do not overlap.
Lower is better. The index adjusts for each fleet's exact age profile; the raw failure rate below does not. The index gap is 9.2 points. Data release dvsa-2024-v1.
Side-by-side evidence
| Measure | Audi A3 | Mercedes A Class |
|---|---|---|
| Age-adjusted MOT Risk Index | 82.1 (81.8–82.5) | 91.3 (90.8–91.8) |
| Raw initial failure rate | 23.11% | 18.83% |
| Dangerous defects per 100 tests | 13.74 | 11.78 |
| Initial tests | 654,933 | 585,107 |
Where their MOT failures diverge
These are component groups present in both models' published top-six failure lists, sorted by the absolute gap. A positive difference means the Audi A3 records more failure items; a negative one means the Mercedes A Class does.
| Component group | Audi A3 | Mercedes A Class | Difference | Lower rate |
|---|---|---|---|---|
| Lamps, reflectors and electrical equipment | 19.1 | 8.8 | +10.3 pp | Mercedes A Class |
| Suspension | 21.7 | 12.7 | +9.0 pp | Mercedes A Class |
| Body, chassis, structure | 9.8 | 2.9 | +6.9 pp | Mercedes A Class |
| Brakes | 11.9 | 8.0 | +3.9 pp | Mercedes A Class |
| Tyres | 12.1 | 11.0 | +1.1 pp | Mercedes A Class |
| Visibility | 11.9 | 11.1 | +0.8 pp | Mercedes A Class |
Counts are defect items, not the share of cars: one failed test can contain several items. A group absent from a model's top six is not treated as zero.
What the six-year test history says
The longitudinal layer follows the same vehicles between MOTs from 2019 to 2024. It separates a one-day retest from the harder question of what returns next year, and puts failures against miles actually driven.
| Component | Audi A3 | Mercedes A Class | Difference | Tracked advisories |
|---|---|---|---|---|
| Steering | 11.0% | 2.9% | +8.1 pp | 4,590 / 6,297 |
| Suspension | 22.4% | 18.5% | +3.9 pp | 235,773 / 43,630 |
| Body, chassis, structure | 19.2% | 15.6% | +3.6 pp | 30,221 / 7,720 |
| Noise, emissions and leaks | 7.7% | 5.7% | +2.1 pp | 61,756 / 7,615 |
| Visibility | 11.5% | 9.5% | +2.0 pp | 1,900 / 1,246 |
| Lamps, reflectors and electrical equipment | 24.6% | 26.1% | -1.5 pp | 31,246 / 5,621 |
| Tyres | 10.2% | 8.8% | +1.4 pp | 485,973 / 281,478 |
| Road wheels | 0.9% | 1.5% | -0.5 pp | 8,505 / 12,273 |
| Brakes | 10.0% | 9.8% | +0.3 pp | 356,663 / 204,031 |
| Seat belts and supplementary restraint systems | 4.0% | 4.3% | -0.2 pp | 7,339 / 4,240 |
| Measure | Audi A3 | Mercedes A Class |
|---|---|---|
| Repaired and passed the same day | 45.6% | 48.3% |
| Passed 1–10 days later | 51.8% | 49.3% |
| Median retest delay | 1.0 days | 1.0 days |
| Failures per 10,000 miles | 0.363 | 0.313 |
| Three-test clean streak | 38.1% | 42.3% |
| Same advisory repeated 3+ times | 29.8% | 20.0% |
Care proxy is descriptive, not a claim about an owner's character: a clean streak means three or more consecutive tests with nothing recorded; the repeat measure means the same advisory appeared at least three times.
Safety recalls
| Model | Campaigns listed | Per 10,000 licensed |
|---|---|---|
| Audi A3 | 26 | 0.60 |
| Mercedes A Class | 100 | 2.64 |
More campaigns do not by themselves mean a less reliable car: recalls are manufacturer remedies, and the licensed-fleet denominator is unavailable for some families. Check a registration for outstanding work before buying.
Do other countries see the same thing?
Both models appear in the same independent national inspection datasets below. Compare each model with that country's own average; absolute pass rates are not portable between rulebooks.
| Country / test | Model | Model fails | National average | Position | Inspections |
|---|---|---|---|---|---|
| Netherlands · APK | Audi A3 | 36.7% | 50.9% | -14.2 pp | 36,920 |
| Netherlands · APK | Mercedes A Class | 43.4% | 50.9% | -7.5 pp | 41,398 |
| Norway · PKK | Audi A3 | 33.9% | 33.5% | +0.4 pp | 5,628 |
| Norway · PKK | Mercedes A Class | 27.5% | 33.5% | -6.0 pp | 1,790 |
Sources are the national PKK, Katsastus and APK datasets recorded in each family artifact. Position is model failure rate minus that country's national rate.
Quick answers
- Is the Audi A3 or the Mercedes A Class more reliable?
- The Audi A3 has the stronger age-adjusted MOT result: index 82.1 against 91.3 for the Mercedes A Class, with non-overlapping 95% confidence intervals.
- Does the Audi A3 or the Mercedes A Class fail more MOTs?
- 23.11% of Audi A3 initial tests and 18.83% of Mercedes A Class initial tests found a failing defect in 2024. The lower raw rate belongs to the Mercedes A Class, but the age-adjusted index is the fairer model comparison because the fleets can be different ages.
- What are the main MOT problem areas on the Audi A3 and Mercedes A Class?
- The leading published failure group for the Audi A3 is suspension at 21.7 items per 100 tests; for the Mercedes A Class it is suspension at 12.7 per 100.
- Should I buy a Audi A3 or a Mercedes A Class?
- If MOT reliability is the deciding factor, the Audi A3 is the evidence-led choice. Still check the individual car's MOT history and condition: these figures describe whole model populations, not a particular vehicle.
Model pages and nearby comparisons
See the Audi A3 and Ford Focus comparisonSee the Audi A3 and Vauxhall Astra comparisonSee the Audi A3 and BMW 3 Series comparison
Browse all car reliability comparisons.
How to read and cite this comparison
Scope: class-4 vehicles, initial tests only, Great Britain 2024. PRS fixed-on-the-spot results count as failures because a defect was present on arrival. Index = observed initial failures ÷ age-profile-expected failures × 100; intervals are 95% confidence intervals. Every model family combines all generations and engines. Full method: methodology.
Cite: MOT Risk Index (2026). Audi A3 vs Mercedes A Class: MOT reliability comparison, 2024 (dvsa-2024-v1). https://motriskindex.co.uk/compare/audi-a3-vs-mercedes-a-class/