Mercedes-Benz 420 MOT Pass Rate
Overall pass rate across all manufacture years, based on 4,393 real MOT test results. Failure rate: 21.6%.
Data from official DVSA MOT testing records
Mercedes-Benz 420 MOT Reliability Overview
The Mercedes-Benz 420 is a niche vehicle in the UK, with 4,393 MOT test results recorded in our database spanning 7 manufacture years. It has an overall MOT pass rate of 78.4% and a failure rate of 21.6%, which is well above the UK average of approximately 37%.
Based on this data, the Mercedes-Benz 420 earns a "Excellent" reliability rating. The average Mercedes-Benz 420 presents for MOT with approximately 102,990 miles on the clock. Manufacture year matters: 1989 models achieve the highest pass rate at 81.5%, while 1992 models have the lowest at 72.1%. This 9.4 percentage point difference suggests notable variation in build quality or component durability across production years.
The most common MOT failure for the Mercedes-Benz 420 is Suspension, affecting 24.8% of all tests. 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. The second most common issue is Brakes at 22.3%. Lamps, reflectors and electrical equipment rounds out the top three at 14.9%. 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 3 vintages — click year chips to highlight.
Multi-line chart showing how different Mercedes-Benz 420 vintages degrade over time, from age 3 to 37 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 | Suspension | 24.8% | 1,091 |
| 2 | Brakes | 22.3% | 981 |
| 3 | Lamps, Reflectors And Electrical Equipment | 18.7% | 823 |
| 4 | Tyres | 8.6% | 377 |
| 5 | Body, Chassis, Structure | 8.1% | 355 |
| 6 | Noise, Emissions And Leaks | 6.9% | 303 |
| 7 | Visibility | 6.4% | 280 |
| 8 | Steering | 5.0% | 218 |
| 9 | Non-component Advisories | 1.7% | 75 |
| 10 | Exhaust, Fuel And Emissions | 1.7% | 73 |
| 11 | Driver's View Of The Road | 1.4% | 62 |
| 12 | Identification Of The Vehicle | 1.1% | 47 |
| 13 | Body, Structure And General Items | 0.8% | 37 |
| 14 | Seat Belts And Supplementary Restraint Systems | 0.6% | 28 |
Failures per 10,000 Miles
avg. 102,990 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 |
|---|---|---|---|
| Suspension | 2.41 | 24.8% | 1,091 |
| Brakes | 2.17 | 22.3% | 981 |
| Lamps & Electrical | 1.82 | 18.7% | 823 |
| Body & Structure | 0.86 | 8.9% | 392 |
| Tyres | 0.83 | 8.6% | 377 |
| Visibility | 0.76 | 7.8% | 342 |
| Noise, emissions and leaks | 0.67 | 6.9% | 303 |
| Steering | 0.48 | 5.0% | 218 |
| Non-component advisories | 0.17 | 1.7% | 75 |
| Emissions & Exhaust | 0.16 | 1.7% | 73 |
| Identification of the vehicle | 0.10 | 1.1% | 47 |
| Seat Belts | 0.06 | 0.6% | 28 |
🚗 Similar Cars to Consider
Mileage at MOT
The average Mercedes-Benz 420 has 102,990 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-Benz 420 has a mileage-adjusted failure rate of 2.10% per 10,000 miles driven. The average across all makes is 5.38%, so this model is better than average.
About Mercedes-Benz 420 MOT Data
The Mercedes-Benz 420 is a niche vehicle in the UK, with 4,393 MOT test results recorded in our database spanning 7 manufacture years. It has an overall MOT pass rate of 78.4% and a failure rate of 21.6%, which is well above the UK average of approximately 37%.
For Mercedes-Benz 420 owners, these results suggest a reliable vehicle that generally passes its MOT without major issues. Focus your pre-MOT checks on suspension and brakes 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.
Suspension — 24.8% of failures
Suspension issues account for 24.8% of MOT failures on the Mercedes-Benz 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.
Brakes — 22.3% of failures
Brakes issues account for 22.3% of MOT failures on the Mercedes-Benz 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).
Lamps, reflectors and electrical equipment — 14.9% of failures
Lamps, reflectors and electrical equipment issues account for 14.9% of MOT failures on the Mercedes-Benz 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-Benz 420?
Based on 4,393 MOT tests in our database, the Mercedes-Benz 420 has an overall pass rate of 78.4% (21.6% fail rate).
What are the most common MOT failures on a Mercedes-Benz 420?
The top 3 reasons a Mercedes-Benz 420 fails its MOT are: 1. Suspension (24.8%), 2. Brakes (22.3%), 3. Lamps, reflectors and electrical equipment (14.9%). Check these areas before booking your MOT.
Is the Mercedes-Benz 420 reliable?
With a 21.6% 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-Benz 420?
Based on failure data, focus on: Suspension (24.8%); Brakes (22.3%); Lamps, reflectors and electrical equipment (14.9%). 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.