Mercedes 420 MOT Pass Rate
Overall pass rate across all manufacture years, based on 6,415 real MOT test results. Failure rate: 31.1%.
Data from official DVSA MOT testing records
Mercedes 420 MOT Reliability Overview
The Mercedes 420 is a less common vehicle in the UK, with 6,415 MOT test results recorded in our database spanning 11 manufacture years. It has an overall MOT pass rate of 68.9% and a failure rate of 31.1%, which is slightly above the UK average of approximately 37%.
Based on this data, the Mercedes 420 earns a "Good" reliability rating. The average Mercedes 420 presents for MOT with approximately 99,693 miles on the clock. Manufacture year matters: 2007 models achieve the highest pass rate at 84.1%, while 1978 models have the lowest at 40.6%. This 43.5 percentage point difference suggests notable variation in build quality or component durability across production years.
The most common MOT failure for the Mercedes 420 is Brakes, affecting 21.9% of all tests. Brake-related failures include worn brake pads, corroded brake discs, leaking brake lines, and faulty brake servos. These are safety-critical components — any brake deficiency will result in an MOT fail. The second most common issue is Suspension at 21.1%. Lamps, Reflectors and Electrical Equipment rounds out the top three at 20.9%. Together, these top 3 failure categories account for a significant portion of all MOT failures for this model.
Top failures across all manufacture years combined. Individual year pages may show different top failures.
What Fails Most
Best Year to Buy
📈 How Each Vintage Ages
Tracking how each manufacture year's MOT pass rate changes as the car ages. Showing 4 vintages — click year chips to highlight.
Multi-line chart showing how different Mercedes 420 vintages degrade over time, from age 3 to 30 years.
Only vintages with 100+ tests in at least 3 different test years are shown. Fleet average is the UK-wide pass rate for all cars at each age.
Pass Rate by Manufacture Year
* High Fail Rate badge indicates an MOT pass rate below 65% (failure rate above 35%).
What Fails on This Car?
Click a category to see specific failure items.
View as table
| Rank | Failure Category | Rate (%) | Count |
|---|---|---|---|
| 1 | Brakes | 30.9% | 1,983 |
| 2 | Lamps, Reflectors And Electrical Equipment | 29.7% | 1,909 |
| 3 | Suspension | 28.3% | 1,815 |
| 4 | Exhaust, Fuel And Emissions | 13.4% | 859 |
| 5 | Tyres | 10.7% | 686 |
| 6 | Driver's View Of The Road | 10.3% | 659 |
| 7 | Steering | 8.7% | 555 |
| 8 | Body, Structure And General Items | 5.8% | 370 |
| 9 | Registration Plates And Vin | 2.2% | 138 |
| 10 | Seat Belts And Supplementary Restraint Systems | 1.9% | 121 |
| 11 | Body, Chassis, Structure | 0.7% | 46 |
| 12 | Non-component Advisories | 0.6% | 36 |
| 13 | Visibility | 0.5% | 33 |
| 14 | Items Not Tested | 0.5% | 30 |
Failures per 10,000 Miles
avg. 99,693 miFor every 10,000 miles driven, this shows what percentage of MOT tests fail for each category. This accounts for how far cars are actually driven, not just raw pass/fail counts.
View as table
| Category | Rate / 10K mi | Raw % | Count |
|---|---|---|---|
| Brakes | 3.10 | 30.9% | 1,983 |
| Lamps & Electrical | 2.98 | 29.7% | 1,909 |
| Suspension | 2.84 | 28.3% | 1,815 |
| Emissions & Exhaust | 1.34 | 13.4% | 859 |
| Visibility | 1.08 | 10.8% | 692 |
| Tyres | 1.07 | 10.7% | 686 |
| Steering | 0.87 | 8.7% | 555 |
| Body & Structure | 0.65 | 6.5% | 416 |
| Registration Plates and VIN | 0.22 | 2.2% | 138 |
| Seat Belts | 0.19 | 1.9% | 121 |
| Non-component advisories | 0.06 | 0.6% | 36 |
| Items Not Tested | 0.05 | 0.5% | 30 |
🚗 Similar Cars to Consider
Mileage at MOT
The average Mercedes 420 has 99,693 miles when tested for MOT.
📊 Mileage-Adjusted Failure Rate
How often this car fails MOT relative to how much it's driven — a fairer comparison than raw pass rate.
The Mercedes 420 has a mileage-adjusted failure rate of 3.12% per 10,000 miles driven. The average across all makes is 5.38%, so this model is better than average.
About Mercedes 420 MOT Data
The Mercedes 420 is a less common vehicle in the UK, with 6,415 MOT test results recorded in our database spanning 11 manufacture years. It has an overall MOT pass rate of 68.9% and a failure rate of 31.1%, which is slightly above the UK average of approximately 37%.
For Mercedes 420 owners, these results suggest a reliable vehicle that generally passes its MOT without major issues. Focus your pre-MOT checks on brakes and suspension for the best chance of a first-time pass. Use our detailed year-by-year breakdown and failure analysis below to understand how your specific 420 is likely to perform.
Brakes — 21.9% of failures
Brakes issues account for 21.9% of MOT failures on the Mercedes 420. Brake-related failures include worn brake pads, corroded brake discs, leaking brake lines, and faulty brake servos. These are safety-critical components — any brake deficiency will result in an MOT fail. Typical repair costs: £150–400. Pre-MOT check: Listen for squealing or grinding noises. Check brake pedal feel — if it feels spongy or goes to the floor, have the system inspected immediately. Look at brake pad thickness through the wheel spokes (minimum 3mm).
Suspension — 21.1% of failures
Suspension issues account for 21.1% of MOT failures on the Mercedes 420. Suspension failures typically involve worn bushes, leaking shock absorbers, broken coil springs, and damaged suspension arms. These affect ride quality, tyre wear, and road holding. Typical repair costs: £200–500. Pre-MOT check: Look for uneven tyre wear, listen for clunking over bumps, and check if the car pulls to one side. A bouncy ride suggests worn shock absorbers. Visually inspect coil springs for cracks.
Lamps, Reflectors and Electrical Equipment — 20.9% of failures
Lamps, Reflectors and Electrical Equipment issues account for 20.9% of MOT failures on the Mercedes 420. Lighting failures cover all external lights: headlights, tail lights, brake lights, indicators, fog lights, and reflectors. A single blown bulb will cause an MOT fail. This is one of the most preventable failure categories. Typical repair costs: £5–50. Pre-MOT check: Walk around the car and check every light — headlights (dipped and main beam), side lights, tail lights, brake lights, indicators, hazard lights, reverse light, rear fog light, and number plate lights. Replace any blown bulbs before the test.
Frequently Asked Questions
What is the MOT pass rate for the Mercedes 420?
Based on 6,415 MOT tests in our database, the Mercedes 420 has an overall pass rate of 68.9% (31.1% fail rate).
What are the most common MOT failures on a Mercedes 420?
The top 3 reasons a Mercedes 420 fails its MOT are: 1. Brakes (21.9%), 2. Suspension (21.1%), 3. Lamps, Reflectors and Electrical Equipment (20.9%). Check these areas before booking your MOT.
Is the Mercedes 420 reliable?
With a 31.1% MOT failure rate, the 420 is more reliable than average compared to the UK average of ~40%.
What should I check before an MOT on my Mercedes 420?
Based on failure data, focus on: Brakes (21.9%); Suspension (21.1%); Lamps, Reflectors and Electrical Equipment (20.9%). These are the areas most likely to cause a fail. Also check all lights, tyres (minimum 1.6mm tread), and windscreen condition — these are quick wins that apply to all cars.
Based on DVSA anonymised MOT test data (2005–2024). Crown copyright, Open Government Licence v3.0.