Model Reports 8 min read Updated 11 Sep 2026 DVSA open data · 5,571 tests analysed

Mercedes-Benz B-Class 2012: reliability & common MOT faults

1,718 first-attempt MOT failures were recorded on the 2012 Mercedes-Benz B-Class in 2025. The items recorded most often on them were Linkage ball joint dust cover (front) and Coil spring (rear). Figures are among first-attempt failed MOT tests, not among all tests.

Petrol B-Class passed first time 6.0 pp more often than diesel ones (73.3% of 1,733 vs 67.3% of 3,838).

First-attempt pass

69.2%

of 5,571 first tests (2025)

First tests

5,571

test year 2025

Failed first attempts

1,718

failed first-attempt tests

Most common fail

13.4%

Linkage ball joint dust cover (front)

MOT pass rates

First-attempt and official-style rates among class 4 first tests of the year.

First-attempt pass

69.2%

of 5,571 first tests (2025)

Official-style pass

74.2%

incl. same-day PRS fixes

First tests

5,571

class 4 · first MOT of the year

Typical age 13.0 yrs · median mileage 85,580 mi

vs 2024: -0.9 pp first-attempt

Note:

  • Class 4 cars · first MOT of the year per vehicle · P/PRS/F outcomes (2025 data).
  • PRS (fixed at the station the same day) counts as a fail in the first-attempt rate.
  • Raw outcomes for this cohort — not adjusted for age, mileage, or peer mix.
  • MOT doesn't test engine or gearbox internals.

Common faults

Failure patterns that show up more often on this registration year than on similar cars.

These MOT failure patterns show up more often on this registration year than on similar cars of the same class, age, and mileage.

Shares below are measured across the 1,717 of 1,718 failed first attempts (99.9%) that recorded an odometer reading in 2025 — the subset the age-and-mileage comparison can be computed on.

Standout: Rigid brake pipes (rear) — 7.0% of this year's failed first attempts

Recorded on 121 of those tests. It tops the table on elevation — about 5.1× more often than on similar cars of the same age and mileage. That is what makes it unusual for its class, which is a different question from what is most likely to fail; the buying checklist ranks by that. The full ranked list is in the table below.

Fault pattern Location Failures vs similar cars Share of fails Confidence
Road Wheels — Condition (front)
Road Wheels > Condition
 Front 48 ×19 2.8% Likely
Rigid brake pipes (rear)
Brakes > Rigid brake pipes
 Rear 121 ×5.1 7.0% Strong
Ball joint dust cover (front)
Suspension > Anti-roll bars > Ball joint dust cover
 Front 96 ×4.0 5.6% Likely
Linkage ball joint dust cover (front)
Suspension > Anti-roll bars > Linkage ball joint dust cover
 Front 230 ×3.6 13.4% Likely
Malfunction indicator lamp
Noise, emissions and leaks > Exhaust emissions > Compression ignition > Malfunction indicator lamp
 Any 93 ×3.1 5.4% Likely
SRS malfunction indicator lamp
Seat belts and supplementary restraint systems > SRS malfunction indicator lamp
 Any 78 ×3.0 4.5% Likely
Coil spring (rear)
Suspension > Springs > Coil springs > Coil spring
 Rear 220 ×3.0 12.8% Possible
Registration plate lamp(s)
Lamps, reflectors and electrical equipment > Registration plate lamp(s)
 Any 133 ×2.3 7.7% Possible
Malfunction indicator lamp
Noise, emissions and leaks > Exhaust emissions > Spark ignition > Malfunction indicator lamp
 Any 109 ×2.2 6.3% Possible

Only patterns that clear minimum sample and elevation thresholds are shown (at least 20 failures and about 2.0× more often than similar cars).

Note: Rates and comparisons are among first-attempt failed tests, not all MOTs. Patterns come from MOT defect codes — not manufacturer service bulletins, recalls, or a diagnosis of any individual car. Failures and advisories are listed separately.

Advisories

Notes recorded at the test that appear more often than on similar cars.

Advisory notes recorded on failed first-attempt tests that appear more often than on similar cars.

Advisory pattern Location Notes vs similar cars Share Confidence
Rigid brake pipes (front)
Brakes > Rigid brake pipes
 Front 105 ×2.5 6.1% Elevated
Rigid brake pipes (rear)
Brakes > Rigid brake pipes
 Rear 162 ×2.5 9.4% Strong
Ball joint (front)
Suspension > Suspension arms > Ball joint
 Front 82 ×2.2 4.8% Elevated
Note: Advisories are not a fail rate — they flag issues noted at the test, often before they become failures.

If you are buying one

What this year's MOT record means for the decision in front of you.

On this year, prefer the petrol. The diesel cars passed first time 6.0 pp less often, on 3,838 tests.

This year also sits 4.6 pp above the midpoint of the 2011 and 2013 cars either side of it — a real break in the model's own run, not the usual year-on-year drift.

Other B-Class years worth knowing about

Newer cars always pass more often, so a plain "best year" list would just rank by age. These are the years that beat or miss the trend their own neighbouring years set — the only age-adjusted signal this data supports.

Year vs the years either side First-attempt pass (rises with newer cars) First tests
2011 B-Class -5.2 pp worse 58.4% 3,257
2014 B-Class -2.2 pp worse 71.5% 7,934

What to check on a 2012 B-Class

The items that failed 2012 B-Class most often, as a share of the year's failed first attempts. This is what goes wrong, not what is unusual — the table further up the page covers that.

  • Linkage ball joint dust cover (front) — recorded on 13.4% of failed first attempts
  • Coil spring (rear) — recorded on 12.8% of failed first attempts
  • Tyres — Condition (front) — recorded on 11.6% of failed first attempts
  • Registration plate lamp(s) — recorded on 7.7% of failed first attempts
  • Rigid brake pipes (rear) — recorded on 7.0% of failed first attempts

Every figure here is a first-attempt MOT rate from DVSA open data for this model line. MOTs do not test engine or gearbox internals, so this is a pre-purchase checklist, not a full reliability score.

FAQs

Short answers about how to read this model-year guide.

Petrol B-Class passed first time 6.0 pp more often than diesel ones (73.3% of 1,733 vs 67.3% of 3,838). In 2025, 69.2% of 5,571 first MOTs on the 2012 Mercedes-Benz B-Class passed first time (PRS — items fixed at the station the same day — counted as a fail). The official-style rate including PRS is 74.2%. Among 1,718 failed first-attempt MOT tests (test year 2025), Rigid brake pipes (rear) appears more often than o…
Ranked by how often they were actually recorded, the items that failed 2012 Mercedes-Benz B-Classs most often at the first attempt were Linkage ball joint dust cover (front) (13.4%), Coil spring (rear) (12.8%) and Tyres — Condition (front) (11.6%) — each as a share of the year's failed first attempts. That is what goes wrong on the car. It is a different question from which patterns are unusual for the class, which…
Among failed first-attempt tests we highlight patterns that appear more often than on similar cars. Top example: Rigid brake pipes (rear) (7.0% of those tests; 121 observed failures; about 5.1× more often than similar cars). These are statistical signals, not a diagnosis of any individual car.
Rigid brake pipes (rear) shows up more often than on similar cars (7.0% of those tests; 121 observed failures; about 5.1× more often than similar cars). That does not prove a design fault — age, mileage, and how the car was used still matter. Treat it as a pre-purchase check point, not a manufacturer service bulletin.
Common MOT problem areas for the 2012 Mercedes-Benz B-Class include Rigid brake pipes (rear), Road Wheels — Condition (front), Ball joint dust cover (front). These patterns show up more often than on similar cars after we filter out sparse noise — not a full list of every possible fault on an individual car.
Advisories flag issues noted at the test and are not a fail rate. We show advisory patterns that appear more often than on similar cars among failed first-attempt tests, separate from common failure rows. Use them as early-warning checks, not as a pass/fail score.
This page highlights MOT failure patterns for the 2012 Mercedes-Benz B-Class (registration year) using UK DVSA open data for the selected test year. Patterns are compared with cars of a similar age and mileage. It is a buyer checklist from MOT defect statistics — not a full service history or manufacturer service-bulletin list.
No. MOT tests do not cover engine internals, gearboxes, or many electronic modules. Patterns here come from MOT defect statistics only and should not be read as engine or gearbox reliability scores.

About this data

How this page is built and what it can (and can't) say.

These figures come from UK MOT open data for this model year. We surface common failure patterns against similar cars — not a full reliability score, and not a pass/fail verdict on any individual vehicle.

2024 2025

What we include

UK Class 4 cars only. Normal MOT tests (not retests); first test per vehicle per calendar year; results pass, PRS, or fail.

Same-day repairs

PRS means the car failed items that were fixed at the test station and then passed the same day. We count PRS as a first-attempt fail in headline rates so same-day repairs do not hide problems.

How we compare

We compare this model year with other Class 4 cars of similar age and mileage in the same test year. This model family is left out of the peer group so the car is not measured against itself.

What this does not cover

  • MOTs do not cover engine internals, gearboxes, or many electronics — this is not a full reliability score.
  • Common faults come from MOT defect stats, not manufacturer TSBs or recalls.
  • Age and mileage matching reduces — but does not remove — differences in how cars were used and maintained.
  • We never invent pass rates, star scores, or ranks when those data marts are missing.

Contains public sector information licensed under the Open Government Licence v3.0.

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