Mercedes Benz 300 MOT Failures
An analysis of 33,463 real DVSA MOT tests on the Mercedes Benz 300 — what fails, how often, and how that compares to every other car on UK roads.
Where the Mercedes Benz 300 fails its MOT
The single biggest MOT failure point on the Mercedes Benz 300 is steering rack wear — this model is 216 times more likely to fail on this item than the average car on UK roads. That makes it an extreme outlier for anyone buying or owning this model. Across 33,463 MOT tests, 3.12% of all Mercedes Benz 300 tests recorded this as a failure.
Steering faults include worn track rod ends, power steering leaks, and rack wear. These are safety-critical — any play in the steering should be investigated immediately.
Other notable weak points include free play in the steering, measured at the rim ... (139x the fleet average), emissions failure (177x the fleet average), subframe bushes or mounts worn (32x the fleet average), and fluid leak (23x the fleet average). These ratios compare the Mercedes Benz 300'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 4 categories: Steering, Exhaust & Emissions, Suspension, Brakes. If you're inspecting a Mercedes Benz 300 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 300'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 300 specifically, the DVSA data shows the most common failures at this mileage are subframe bushes or mounts worn (32x the average) and wheel bearings worn (18x). fluid leak (8.7x) and brake hoses perished or damaged (7.2x) 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 300 specifically, the DVSA data shows the most common failures at this mileage are steering rack wear (216x the average) and free play in the steering, measured at the rim ... (139x). emissions failure (134x) and brakes imbalance across an axle (71x) 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 300 specifically, the DVSA data shows the most common failures at this mileage are seat mounting fault (349x the average) and emissions failure (177x). steering rack wear (71x) and free play in the steering, measured at the rim ... (64x) also appear frequently.
The shift from subframe bushes or mounts worn at lower mileages to seat mounting fault at higher mileages is typical — early failures tend to be design or factory-related, while high-mileage failures reflect accumulated mechanical wear. A car that's been well maintained will usually dodge the worst of both.
What to check before buying a Mercedes Benz 300
Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a Mercedes Benz 300:
Steering — check for steering rack wear, free play in the steering, measured at the rim .... Exhaust & Emissions — check for emissions failure, fluid leak. Suspension — check for subframe bushes or mounts worn, wheel bearings worn.
Always check the car's full MOT history for patterns — recurring advisories often become failures within 12 months. Enter any reg into our free car check to see the complete picture.
Looking at a specific Mercedes Benz 300?
Enter the reg to see its full MOT history, mileage records, write-off status, and finance checks.
Mercedes Benz 300 MOT FAQs
What are the most common MOT failures on a Mercedes Benz 300?
Based on 33,463 DVSA MOT tests, the most common failure is steering rack wear — at 216x the national fleet average. Other frequent failures include free play in the steering, measured at the rim ... and emissions failure.
Is the Mercedes Benz 300 reliable based on MOT data?
The Mercedes Benz 300 has 15 categories where it fails more often than average. The main concern is steering rack wear. 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 300 most commonly fails on seat mounting fault and emissions failure. Under 60,000 miles, the main issues are subframe bushes or mounts worn and wheel bearings worn.
How do I check a Mercedes Benz 300'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.