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UNEXPECTED: New study reveals Top 10 most common causes of MOT failures

New research has shown the most common causes for MOT failures in the UK, with some unexpected features making the top ten.  

Insurance broker One Sure Insurance analysed the DVLA's MOT database to find the most common causes of MOT failure among Class 4 vehicles (cars, vans, motorhomes, and other smaller commercial vehicles).

Taking first place as the most common reason for a car to fail its MOT are worn or damaged tyres. Across all four tyres, poor condition, or not meeting the legal requirement of at least 1.6mm of tread depth contributed to 1,101,839 MOT failures across the UK in a single year. The driver-side front tyre tread depth accounted for more than a quarter of these, the equivalent of 368,853 MOT failures.

In second place, the cause of 1,069,069 MOT failures are damaged coil springs located in your car's suspension. It's no secret that Britain’s roads aren't the smoothest, and the car’s suspension tends to take the brunt of any potholes and speedbumps that road users might encounter on their travels. Fractured or broken front passenger side coil springs accounted for 346,383 of MOT failures in this category.

Headlamp aim takes third place, as the cause of 806,993 MOT failures. Headlamp aim being incorrect, too high or too low, can impact visibility not just for the driver but other users on the road. Headlights can become mis-aligned for several reasons, including damage to the fittings or headlight bulbs simply expanding with age on older cars. The projected beam being incorrect is the leading cause of failure in this category, accounting for 433,681 MOT failures.

Windscreen wipers take fourth place, having caused 778,244 MOT failures, with almost every case of failure being down to the wipers not clearing the windscreen effectively. Wipers not cleaning the windscreen effectively accounts for 751,881 MOT failures within this category.

Position lamps take the fifth spot. Known more commonly as sidelights, non-road safe position lamps have caused 759,032 MOT failures. Used to indicate the size and the position of a car, non-working position lamps make up the bulk of the failures within this category, having caused 710,180 MOT failures.

Brake pads take sixth place, being the cause of 674,986 MOT failures. The leading cause of failure within this category is almost entirely brake pads being less than 1.5mm thick, resulting in 615,077 of these MOT failures.

Seventh place goes to pins and bushes, which caused 632,061 MOT failures. Most failures in this category were due to pins or bushes being excessively worn at the front of the vehicle, resulting in 467,118 of these MOT failures. Bushes act as small protective pads fitted to various parts of the suspension system, and pins – sometimes known as swivel pins, or kingpins – are the main pivot in the steering mechanism of a car or other vehicle.

Ball joints allow suspension movement which maximizes the tyre’s contact with the road providing optimum vehicle control and tire wear. They also take the eighth spot on the list, having caused 620,900 MOT failures. Many original equipment ball joints are designed as sealed units. If the protective boot fails, water and road debris will quickly cause wear and ball joint failure.

Ninth place on the list goes to service brake performance. Otherwise known as the braking system in a vehicle, inadequate service brake performance has resulted in 615,329 MOT failures.

Taking the final spot on the list, in tenth place, are issues with the rigid brake pipes which caused 522,429 MOT failures. These pipes are used to transfer pressurised brake fluid from the master cylinder to the brake hoses and are especially susceptible to corrosion. 143,600 MOT failures were found to be due to the vehicle’s rigid brake pipes being excessively corroded.

Interestingly, the driver's side tyre depth being below 1.6mm is the single most significant cause for failure of an MOT, with 368,853 MOT failures. According to a YouGov poll, Britons are most likely to change their tyres only when it is absolutely necessary. Three in five car owners (60%) switch them out only when carrying on using them becomes untenable, which helps explain why they are the biggest cause of an MOT failure.

The study also found that of the 38,155,866 MOT tests carried out on all classes of vehicles in 2021, almost one in five resulted in failure.

A spokesperson for One Sure Insurance said: "The research sheds light on critical areas of concern for vehicle owners. The results can be helpful for drivers who want to keep their vehicles in good condition and pass the MOT inspection with flying colours.

“It's essential for all drivers to take note of these findings and address any potential issues before an inspection. This proactive approach can help drivers avoid expensive repairs in the future and keep their cars running safely on the road."


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