1991 Mercedes-Benz 420 MOT Pass Rate
Pass rate for 420 models manufactured in 1991, based on 154 real MOT test results.
Data from official DVSA MOT testing records
1991 Mercedes-Benz 420 MOT Analysis
The 1991 Mercedes-Benz 420 has an MOT pass rate of 72.1% based on 154 tests — above the UK average for UK vehicles. Cars of this vintage present for MOT with an average of 131,079 miles on the odometer. With a 27.9% failure rate, the 1991 420 is rated as "Very Good" for MOT reliability.
The leading cause of MOT failure for the 1991 Mercedes-Benz 420 is Brakes, responsible for 5.2% of failures. 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 range from £150–400. Noise, emissions and leaks is the second most common issue at 3.9%. Lamps, reflectors and electrical equipment follows at 2.6%.
Top failures specific to 1991 models only. The overall 420 page may show different rankings.
What Fails Most
What Fails on This Car?
Click a category to see specific failure items.
View as table
| Rank | Failure Category | Rate (%) | Count |
|---|---|---|---|
| 1 | Brakes | 5.2% | 8 |
| 2 | Noise, Emissions And Leaks | 3.9% | 6 |
| 3 | Lamps, Reflectors And Electrical Equipment | 2.6% | 4 |
| 4 | Tyres | 2.6% | 4 |
| 5 | Steering | 1.3% | 2 |
| 6 | Visibility | 1.3% | 2 |
Failures per 10,000 Miles
avg. 131,079 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 | 0.40 | 5.2% | 8 |
| Noise, emissions and leaks | 0.30 | 3.9% | 6 |
| Lamps & Electrical | 0.20 | 2.6% | 4 |
| Tyres | 0.20 | 2.6% | 4 |
| Steering | 0.10 | 1.3% | 2 |
| Visibility | 0.10 | 1.3% | 2 |
Mileage Statistics
Mileage-adjusted failure rate — accounts for how much this model year is typically driven.
About This Data
The 1991 Mercedes-Benz 420 has an MOT pass rate of 72.1% based on 154 tests — above the UK average for UK vehicles. Cars of this vintage present for MOT with an average of 131,079 miles on the odometer. With a 27.9% failure rate, the 1991 420 is rated as "Very Good" for MOT reliability.
If you own or are considering buying a 1991 Mercedes-Benz 420, you can expect reliable MOT performance overall. Before your MOT, pay particular attention to brakes: 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). With an average mileage of 131,079 miles, these vehicles are in the higher-mileage bracket where wear-related failures become more common.
Brakes — 5.2% of failures
Brakes issues account for 5.2% of MOT failures on 1991 Mercedes-Benz 420 models. 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).
Noise, emissions and leaks — 3.9% of failures
Noise, emissions and leaks issues account for 3.9% of MOT failures on 1991 Mercedes-Benz 420 models. Emissions failures occur when exhaust gases exceed legal limits for carbon monoxide (CO), hydrocarbons (HC), or particulate matter (diesel). Common causes include faulty oxygen sensors, clogged catalytic converters, or DPF issues on diesel vehicles. Typical repair costs: £100–1,000+. Pre-MOT check: If the engine management light is on, get it diagnosed before the MOT. For diesel cars, ensure the DPF has completed a regeneration cycle. Regular servicing and using premium fuel before the test can help.
Lamps, reflectors and electrical equipment — 2.6% of failures
Lamps, reflectors and electrical equipment issues account for 2.6% of MOT failures on 1991 Mercedes-Benz 420 models. 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.
Based on DVSA anonymised MOT test data (2005–2024). Crown copyright, Open Government Licence v3.0.