Model Reports 8 min read Updated 11 Sep 2026 DVSA open data · 3,849 tests analysed

Mercedes-Benz B-Class 2009: reliability & common MOT faults

1,623 first-attempt MOT failures were recorded on the 2009 Mercedes-Benz B-Class in 2025. The items recorded most often on them were Drive shafts — Joints (front) and Ball joint (front). Figures are among first-attempt failed MOT tests, not among all tests.

Petrol B-Class passed first time 4.7 pp more often than diesel ones (60.1% of 1,964 vs 55.4% of 1,885).

First-attempt pass

57.8%

of 3,849 first tests (2025)

First tests

3,849

test year 2025

Failed first attempts

1,623

failed first-attempt tests

Most common fail

14.6%

Drive shafts — Joints (front)

MOT pass rates

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

First-attempt pass

57.8%

of 3,849 first tests (2025)

Official-style pass

65.0%

incl. same-day PRS fixes

First tests

3,849

class 4 · first MOT of the year

Typical age 16.0 yrs · median mileage 95,788 mi

vs 2024: +1.9 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 1,620 of 1,623 failed first attempts (99.8%) that recorded an odometer reading in 2025 — the subset the age-and-mileage comparison can be computed on.

Standout: Service brake performance — 2.7% of this year's failed first attempts

Recorded on 44 of those tests. It tops the table on elevation — about 5.8× 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.

No patterns met the strongest callout thresholds on this page; showing the highest-lift rows that still cleared the display floors.

Fault pattern Location Failures vs similar cars Share of fails Confidence
Service brake performance
Brakes > Brake performance > Service Brake Efficiency (sp) > Rbt (sp) > Service brake performance
 Any 44 ×5.8 2.7% Likely
Rigid brake pipes (rear)
Brakes > Rigid brake pipes
 Rear 127 ×4.4 7.8% Likely
Side repeaters (front)
Lamps, reflectors and electrical equipment > Direction indicators > Flashing type > Side repeaters
 Front 96 ×3.7 5.9% Likely
Drive shafts — Joints (front)
Body, chassis, structure > Transmission > Drive shafts > Joints
 Front 237 ×2.9 14.6% Possible
Diesel emissions test (compression-ignition rules for vehicles from 01/07/2008) Any 70 ×2.4 4.3% Possible
Individual direction indicators (rear)
Lamps, reflectors and electrical equipment > Direction indicators > Flashing type > Individual direction indicators
 Rear 78 ×2.4 4.8% Possible
Coil spring (rear)
Suspension > Springs > Coil springs > Coil spring
 Rear 144 ×2.3 8.9% Possible
Shock absorbers (front)
Suspension > Shock absorbers
 Front 79 ×2.2 4.9% 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.

Wear patterns

Usage and mileage effects that often track road use rather than model design.

These patterns look like wear or usage effects rather than model-specific design faults. Tyres, brake friction material, and alignment-related defects often track mileage and road use.

Pattern Location Failures vs similar cars Share of fails Confidence
Brake discs (rear)
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Rear 39 ×2.3 2.4% Wear
Note: These patterns are not treated as a model design fault in our common-faults ranking.

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 (rear)
Brakes > Rigid brake pipes
 Rear 259 ×3.3 16.0% Likely
Flexible brake hoses (front)
Brakes > Flexible brake hoses
 Front 60 ×3.1 3.7% Elevated
Rigid brake pipes (front)
Brakes > Rigid brake pipes
 Front 119 ×2.5 7.3% Elevated
Seat belts — Condition (rear)
Seat belts and supplementary restraint systems > Seat belts > Condition
 Rear 25 ×2.4 1.5% Possible
Individual direction indicators (rear)
Lamps, reflectors and electrical equipment > Direction indicators > Flashing type > Individual direction indicators
 Rear 57 ×2.3 3.5% Possible
Brake pads (rear)
Brakes > Mechanical brake components > Brake linings and pads > Brake pads
 Rear 121 ×2.2 7.5% Wear
Brake discs
Brakes > Mechanical brake components > Brake discs and drums > Brake discs
 Any 27 ×2.0 1.7% Wear
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 4.7 pp less often, on 1,885 tests.

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
2012 B-Class +4.6 pp better 69.2% 5,571
2011 B-Class -5.2 pp worse 58.4% 3,257

What to check on a 2009 B-Class

The items that failed 2009 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.

  • Drive shafts — Joints (front) — recorded on 14.6% of failed first attempts
  • Ball joint (front) — recorded on 12.3% of failed first attempts
  • Rbt (sp) — recorded on 11.2% of failed first attempts
  • Coil spring (rear) — recorded on 8.9% of failed first attempts
  • Linkage ball joint dust cover (front) — recorded on 8.1% 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 4.7 pp more often than diesel ones (60.1% of 1,964 vs 55.4% of 1,885). In 2025, 57.8% of 3,849 first MOTs on the 2009 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 65.0%. Among 1,623 failed first-attempt MOT tests (test year 2025), Service brake performance appears more often than…
Ranked by how often they were actually recorded, the items that failed 2009 Mercedes-Benz B-Classs most often at the first attempt were Drive shafts — Joints (front) (14.6%), Ball joint (front) (12.3%) and Rbt (sp) (11.2%) — 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 the common-faults table a…
Among failed first-attempt tests we highlight patterns that appear more often than on similar cars. Top example: Service brake performance (2.7% of those tests; 44 observed failures; about 5.8× more often than similar cars). These are statistical signals, not a diagnosis of any individual car.
Service brake performance shows up more often than on similar cars (2.7% of those tests; 44 observed failures; about 5.8× 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 2009 Mercedes-Benz B-Class include Service brake performance, Rigid brake pipes (rear), Side repeaters (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 2009 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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