Used car guide

2018 Mercedes-Benz B-Class: common problems and what to check

What gets flagged at MOT on 2018 Mercedes-Benz B-Classs, from 3,892 tests in 2025, plus known faults and what to look at before you buy one.

3,892MOT tests in 2025
83%pass first time (all 2018 cars: 81%)
5,800typical miles a year
2.7×the usual rate for number plate lights

What stands out

Parts flagged at MOT more often on 2018 Mercedes-Benz B-Classs than on all cars registered in 2018.

  • Number plate lights2.7× usual
    Mercedes-Benz B-Class
    4.9% All 2018 cars
    1.8%

    Failed outright at MOT: 2.6%, against 0.6% of all 2018 cars. The rest were advisories or minor defects.

    Rough price £5–£40 our estimate

    At the viewing: Check the number plate lights work and the plates are clean and legal.

By area

The share of 2018 Mercedes-Benz B-Class MOT tests where testers flagged each area, as a fail or an advisory. Rough prices are typical independent-garage costs.

  • Tyres
    31% of testsRough price £70–£150

    At the viewing: Check the tread on all four tyres, including the inside edges, and look for cracks or bulges.

  • Brakes
    15% of testsRough price £150–£350

    At the viewing: Look for a lip on the disc edges and feel for judder or pulling when braking firmly from about 40mph.

  • Lights and electrics
    8% of testsRough price £10–£80

    At the viewing: Ask a friend to check every light, including brake lights and indicators, while you operate them.

  • Wipers, windscreen and mirrors
    5% of testsRough price £15–£250

    At the viewing: Check for chips in the driver's view, and test the wipers and washers.

  • Suspension
    5% of testsRough price £120–£400

    At the viewing: Listen for knocks over speed bumps, and look behind each front wheel for a snapped coil spring.

  • Seats and seatbelts
    3% of testsRough price £80–£250

    At the viewing: Pull each seatbelt sharply. It should lock, and retract cleanly.

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Other years

YearMOT testsMost flagged
2019599Tyres 25%
20175,689Tyres 29%
20165,353Tyres 31%
20155,654Tyres 32%
20148,185Tyres 32%
20136,957Tyres 33%
20125,658Tyres 32%
20113,373Brakes 42%
20104,279Brakes 44%
20093,989Brakes 48%
20083,072Brakes 51%
20072,249Brakes 47%
20061,611Brakes 51%

Where this comes from: the DVSA's anonymised results for every MOT test in Great Britain in 2025, counting tests of 2018 Mercedes-Benz B-Classs registered in 2018. "Flagged" includes advisories, so it isn't the same as a fail rate. How we score