The picture
79.13% pass rate hides a tyre and spring story
Tyre tread depth is the A-Class's most common MOT failure — unusual for a car that averages only 64,079 miles at test time. Spring fractures and windscreen damage follow. At 79.13% across 293,073 tests, the A-Class is one of the better performers in the compact premium class, though that pass rate depends heavily on owners keeping up with tyres they often ignore on a prestige car.
Owner reports paint a different picture of day-to-day reliability. Speed Limit Assist faults, driver display failures within days of delivery, and repeated black screens on the instrument cluster all feature. One dealer kept a car for three weeks chasing an MBUX software issue. None of that fails an MOT — but an underpressure tyre or a stone chip across the A-pillar sightline will. Check the rubber, check the glass, inspect the springs. The A-Class passes when its owner pays attention.
Top ten reasons for rejection.
- 01
Tyre tread depth not in accordance with the requirements
7,497 occurrences · 2.6% of tests
- 02
A spring or spring component fractured or seriously weakened
7,412 occurrences · 2.5% of tests
- 03
Windscreen or window damaged or seriously discoloured but not adversely affecting driver's view
6,178 occurrences · 2.1% of tests
- 04
a brake lining or pad worn below 1.5mm
5,166 occurrences · 1.8% of tests
- 05
A tyre seriously damaged
4,321 occurrences · 1.5% of tests
- 06
A tyre cords visible or damaged
3,944 occurrences · 1.3% of tests
- 07
A transmission shaft constant velocity joint boot severely deteriorated
3,747 occurrences · 1.3% of tests
- 08
Windscreen washers not working or not providing sufficient fluid to clear the windscreen
3,734 occurrences · 1.3% of tests
- 09
A suspension joint dust cover severely deteriorated
3,688 occurrences · 1.3% of tests
- 10
An SRS malfunction indicator lamp (MIL) indicates a system malfunction
3,462 occurrences · 1.2% of tests
Counts cover Major and Dangerous defects logged at test. Advisory items excluded so this shows why a car was rejected, not just what the tester flagged in passing.
Worst-case fix budget · top 3 failures
£220–£495
If every one of this A Class's most-logged Major fails hit at the same MOT, that's the real-world UK garage range. Reality is usually one or two items, not all of them. Open the estimator →
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Tools that pre-empt a retest.
Picked against this car's top failure patterns. Affiliate links to Amazon UK — we earn a small cut at no cost to you. Disclosed up-front, doesn't shape the data.
Item 01 · Amazon UK
Digital tyre-tread depth gauge
Five quid for a gauge beats £150 for a retest. UK MOT minimum is 1.6mm — most testers fail anything below 2mm to be safe.
Search Amazon UK
Item 02 · Amazon UK
Brake pad measurement gauge
Testers fail pads under 1.5mm. A wear gauge tells you if you've got two months left or two weeks.
Search Amazon UK
Owner reports · Honest John
What owners actually report.
Verbatim faults logged by owners on honestjohn.co.uk over recent years. We didn't summarise — these are the words people typed in.
What's good
Innovative infotainment system that looks great. Interior looks pretty swish. Comfortable and easy to drive.
Recent owner-reported faults
- 5 Apr 2020
Reports of issues with reader's Mercedes-Benz A-Class. Dealer's had the car for three weeks: 1. Speed Limit Assist feature not working correctly. This feature is designed to keep the driver informed of the prevailing speed limit at all times. The fault manifests itself in a number of different ways but one simple example is driving past a de-restriction sign will sometimes correctly show the 60mph limit symbol on the dash until the next speed limit sign or on other occasions it will show a de-restriction symbol for 10 seconds followed by no symbol. 2. Active Lane Assist, designed to sense when the vehicle is unintentionally crossing a white line and applying the brakes on one side to keep the vehicle in lane, however, this frequently senses things other than white lines. These might be lines of shiny bitumen, rivulets of water or boxes around bus stops which means that when it senses these the brakes are incorrectly applied which can be dangerous. 3. New problem introduced by software update FU2/063, Personal POI's do not give Visual or Audible Warnings. This worked correctly on the previous release of software. 4. Easy Entry/Exit, seat not working correctly. This feature is intended to position the drivers seat for Easy Entry/Exit then move it to the driving position when the ignition is switched on. Intermittent problem where when entering the car and switching the ignition on the seat briefly moves backwards and then returns to the Easy Entry/Exit position. 5. Top LED dash strip not as bright as other LED strips. The strip has been replaced twice and is now better than it was originally. The dealer agrees that this is not correct but has no solution. 6. When turning at low speed proximity sensors report non-existent hazards. Turning right off a main road, if a vehicle has just passed on the right the proximity alarm will sound continually as you start to turn despite the passing vehicle having already gone past, indeed the alarm seems to be locked on for about 5 seconds. This is exceedingly distracting and therefore dangerous but Mercedes have no solution. 7. A plastic rather than metallic rattle from somewhere at the back of the car. Several attempts have been made to correct this without success.
- 3 Oct 2019
Report of failure of driver display on new 2019/69 Merceded Benz A 220 AMG Premium Plus a couple of days after purchase.
- 30 Aug 2019
Report of repeated failure of driver instrument display of 2019 Mercedes-Benz A250 bought as an ex-demonstrator at 3,500 miles in June 2019. Frequently it does not switch on leaving a black screen in front of the driver with no means of viewing the speedo, petrol guage, or ensuring the transmission is in reverse, drive or park.
Source: honestjohn.co.uk · 3 reports indexed
Buying or keeping a A Class?
Use the failure ranking as a pre-test checklist or a haggling lever. Treat the headline pass rate as a fleet-wide trend, not a guarantee on any individual car.
If you own a A Class and your last MOT looked nothing like the ranked failures above, that's normal — individual cars vary widely. The ranking shows the patterns testers flag most often across the country.