Mercedes Benz B Class MOT Failures
An analysis of 308,692 real DVSA MOT tests on the Mercedes Benz B Class — what fails, how often, and how that compares to every other car on UK roads.
Where the Mercedes Benz B Class fails its MOT
The single biggest MOT failure point on the Mercedes Benz B Class is emissions failure — this model is 71 times more likely to fail on this item than the average car on UK roads. That makes it a major concern for anyone buying or owning this model. Across 308,692 MOT tests, 0.93% of all Mercedes Benz B Class tests recorded this as a failure.
Exhaust and emissions failures often point to catalytic converter degradation, lambda sensor faults, or — in diesel models — DPF problems. These can be expensive to fix and will cause an immediate MOT failure.
Other notable weak points include fuel pipe or hose damaged (91x the fleet average), any fracture or welding defect on a wheel (24x the fleet average), light unit fault (32x the fleet average), and service brake efficiency below minimum requirement (28x the fleet average). These ratios compare the Mercedes Benz B Class's failure rate on each item against the national average for all cars tested — a ratio of 10x means this model fails ten times more often than a typical car.
The failures span 5 categories: Exhaust & Emissions, Bodywork, Wheels, Lights & Electrics, Brakes. If you're inspecting a Mercedes Benz B Class before purchase, these are the areas to focus on — and if any have been flagged as advisories on a previous MOT, they're likely to become failures in the near future.
How failures change with mileage
The Mercedes Benz B Class's weak points shift as the car covers more miles. Understanding these patterns helps you know what to expect — and what to budget for — at each stage of ownership.
Under 60,000 miles
At this mileage, most failures are either design-related or caused by age rather than wear. Components like bushes and drop links may not have been replaced yet, and original-fit parts can deteriorate even on low-mileage cars that spend a lot of time sitting.
For the Mercedes Benz B Class specifically, the DVSA data shows the most common failures at this mileage are fuel pipe or hose damaged (91x the average) and brake hoses perished or damaged (60x). transmission shaft constant velocity joint boot... (26x) and service brake efficiency below minimum requirement (21x) also appear frequently.
60,000 to 100,000 miles
This is where routine wear items start to show up. Brake components, tyres, and exhaust parts have done serious work by this point. Cars that have been well serviced will show fewer of these failures — this mileage band is where good maintenance really separates the well-kept from the neglected.
For the Mercedes Benz B Class specifically, the DVSA data shows the most common failures at this mileage are fuel pipe or hose damaged (36x the average) and any part of the noise suppression system insecure (29x). fuel system leaking, or missing or ineffective ... (27x) and any fracture or welding defect on a wheel (24x) also appear frequently.
Over 100,000 miles
High-mileage cars accumulate failures across multiple systems. The key question isn't whether things will need doing — they will — but whether the car has been maintained well enough to keep on top of them. Look for a consistent service history and recent MOT passes with minimal advisories.
For the Mercedes Benz B Class specifically, the DVSA data shows the most common failures at this mileage are fuel pipe or hose damaged (29x the average) and any fracture or welding defect on a wheel (23x). service brake efficiency below minimum requirement (22x) and headlight fault (21x) also appear frequently.
What to check before buying a Mercedes Benz B Class
Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a Mercedes Benz B Class:
Exhaust & Emissions — check for emissions failure. Bodywork — check for fuel pipe or hose damaged, fuel system leaking, or missing or ineffective ..., transmission shaft constant velocity joint boot.... Wheels — check for any fracture or welding defect on a wheel. Lights & Electrics — check for light unit fault.
Always check the car's full MOT history for patterns — recurring advisories often become failures within 12 months. And verify the service history to confirm maintenance has been kept up to schedule. Enter any reg into our free car check to see the complete picture.
Looking at a specific Mercedes Benz B Class?
Enter the reg to see its full MOT history, mileage records, write-off status, and finance checks.
Mercedes Benz B Class MOT FAQs
What are the most common MOT failures on a Mercedes Benz B Class?
Based on 308,692 DVSA MOT tests, the most common failure is emissions failure — at 71x the national fleet average. Other frequent failures include fuel pipe or hose damaged and any fracture or welding defect on a wheel.
Is the Mercedes Benz B Class reliable based on MOT data?
The Mercedes Benz B Class has 19 categories where it fails more often than average. The main concern is emissions failure. Always check a specific car's full history before buying.
What MOT failures should I expect at high mileage?
Above 100,000 miles, the Mercedes Benz B Class most commonly fails on fuel pipe or hose damaged and any fracture or welding defect on a wheel. Under 60,000 miles, the main issues are fuel pipe or hose damaged and brake hoses perished or damaged.
How do I check a Mercedes Benz B Class's MOT history?
Enter the registration number into our free car check above. You'll see every MOT test result, advisories and failures, mileage readings, write-off status, and finance checks.
MOT failure data sourced from DVSA bulk test records via data.gov.uk. Ratios compare this model's failure rate against the national fleet average. Known issues sourced from manufacturer bulletins, specialist workshops, and verified owner reports.