Mercedes Benz 420 MOT Failures
An analysis of 4,724 real DVSA MOT tests on the Mercedes Benz 420 — what fails, how often, and how that compares to every other car on UK roads.
Where the Mercedes Benz 420 fails its MOT
The single biggest MOT failure point on the Mercedes Benz 420 is subframe bushes or mounts worn — this model is 32 times more likely to fail on this item than the average car on UK roads. That makes it a significant weak point for anyone buying or owning this model. Across 4,724 MOT tests, 11.26% of all Mercedes Benz 420 tests recorded this as a failure.
Suspension failures typically mean worn bushes, drop links, or dampers. These affect handling and tyre wear. Budget £150–£400 per corner at an independent garage for full suspension overhaul.
Other notable weak points include suspension joint dust cover missing or no longe... (21x the fleet average), suspension joint dust cover severely deteriorated (24x the fleet average), free play in the steering, measured at the rim ... (46x the fleet average), and fluid leak (7.0x the fleet average). These ratios compare the Mercedes Benz 420'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: Suspension, Steering, Exhaust & Emissions, Brakes. If you're inspecting a Mercedes Benz 420 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 420'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.
The standout failure at this mileage is suspension joint dust cover severely deteriorated at 24x the fleet average.
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 420 specifically, the DVSA data shows the most common failures at this mileage are subframe bushes or mounts worn (32x the average) and suspension joint dust cover missing or no longe... (21x). exhaust system damage (5.0x) and exhaust system damage 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 420 specifically, the DVSA data shows the most common failures at this mileage are free play in the steering, measured at the rim ... (46x the average) and subframe bushes or mounts worn (12x). suspension joint dust cover severely deteriorated (8.7x) and suspension joint dust cover missing or no longe... (7.0x) also appear frequently.
The shift from suspension joint dust cover severely deteriorated at lower mileages to free play in the steering, measured at the rim ... 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 420
Based on the MOT failure data and known issues above, here's what to prioritise when inspecting a Mercedes Benz 420:
Suspension — check for subframe bushes or mounts worn, suspension joint dust cover missing or no longe..., suspension joint dust cover severely deteriorated. Steering — check for free play in the steering, measured at the rim ..., track rod ends 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 420?
Enter the reg to see its full MOT history, mileage records, write-off status, and finance checks.
Mercedes Benz 420 MOT FAQs
What are the most common MOT failures on a Mercedes Benz 420?
Based on 4,724 DVSA MOT tests, the most common failure is subframe bushes or mounts worn — at 32x the national fleet average. Other frequent failures include suspension joint dust cover missing or no longe... and suspension joint dust cover severely deteriorated.
Is the Mercedes Benz 420 reliable based on MOT data?
The Mercedes Benz 420 has 10 categories where it fails more often than average. The main concern is subframe bushes or mounts worn. 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 420 most commonly fails on free play in the steering, measured at the rim ... and subframe bushes or mounts worn. Under 60,000 miles, the main issues are suspension joint dust cover severely deteriorated.
How do I check a Mercedes Benz 420'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.