The most common MOT failure reasons - and how you can avoid them
More than a quarter of all cars tested initially fail their MOT every year. We share the most common causes of failure and how you can prevent them...
Around 30 million MOT tests are conducted across the UK each year, with more than a quarter initially resulting in failure. Despite MOT testers checking an extensive range of components, the majority of failures are caused by the same issues.
The good news is that many of these can be easily identified with some quick and easy checks at the roadside before you take your car in for its MOT.
Here, we share the most common reasons why cars failed their MOTs during 2024, according to official data from the Driver and Vehicle Standards Agency (DVSA), and the checks you can make to your vehicle to boost your chances of passing.
1. Suspension – 18.8%
According to the DVSA, faulty suspension components are the most common cause for MOT failures by the narrowest of margins. During the MOT, your car’s suspension system will undergo thorough examination to make sure that everything is in full working order, there is no excessive corrosion and that parts such as the shock absorbers are not leaking.
Making sure the suspension is in tip top condition is vital because driving a car with broken components can severely affect the stability and handling of a vehicle, and could result in a serious accident.
The easiest way to reduce the chances of your car failing its MOT due to faulty suspension components is by pressing down on each corner of the vehicle. When you release pressure, the car should quickly spring back into its normal position, sitting level. You should also take the car for a short drive and listen for any unusual noises when travelling over bumps in the road.
2. Tyres – 18.5%
All road legal cars must have tyres in good condition to prevent the risk of skidding, particularly when travelling on wet or icy roads, or high-speed blowouts. However, since tyres can wear more quickly than many other components, they’re a common cause for MOT failures.
Before driving to the test centre, use a portable tyre pressure gauge or machine at your local petrol station to make sure that the amount of air in each tyre matches the level recommended by the manufacturer. Similarly, use a depth gauge or the outer ring of a 20p coin to make sure the grooves within the tyre exceed 1.5mm – the legal limit for tyre depth.
It’s also worth making sure that there aren’t any cracks within the side wall, which typically form when tyre rubber is starting to age. These cracks are often small but can seriously affect the rigidity of the tyres and increase the risk of a blowout when travelling at high-speed.
3. Brakes – 17.8%
It comes as no surprise that your car’s brakes will undergo rigorous testing during its MOT to make sure the vehicle comes to a complete stop in as short a distance as possible. In particular, the efficiency of each brake (including the handbrake), the condition of replaceable components and the effectiveness of safety systems, such as anti-lock brakes (ABS) and electronic stability control (ESC) will be checked.
Some of these components can be expensive to replace; however, one of the most common brake related issues encountered during an MOT is due to worn-out pads, which typically cost between £100 and £300 for a new set at a main dealer. While brake pads can last beyond 50,000 miles, you should regularly check for signs that your car needs a new set.
Most notably, many modern cars feature brake pad monitoring sensors that will display a dashboard warning light if they’re worn beyond a certain point. During a service, the mechanic should also check the condition of the pads to make sure they don’t fall short of the minimum depth requirement of 1.5mm (although 3mm is generally recommended).
4. Lights, reflectors and electrics – 13.3%
While the inspector won’t check every electronic device fitted to the car, they will make sure that all essential components are working properly. This includes all of the exterior lights fitted to the vehicle.
As a result, it’s important that you check your lights before driving the car to the garage. The easiest way to do this is by turning on each set of lights separately seeing whether they light up. This will include the headlights, brake lights and indicators, but don’t forget that the rear foglights (and front foglights if the car was first registered after 1 March 2018), registration plate lamps and side indicator repeaters will also need to be in full working order for the car to pass.
The examiner will also inspect the condition of the battery during the MOT, so if you have any issues starting the engine, it’s worth getting it checked and, if necessary, replaced to avoid having to pay for a retest.
5. Body, chassis and structure – 7.6%
While your car won’t fail its MOT if the bodywork has minor dents or scratches, it won’t pass if there are serious forms of damage. A vehicle will fail if accident damage has resulted in sharp or jagged edges that could pose an increased risk to other road users in an accident or has reduced its structural integrity.
However, the main reason why cars fail over bodywork and chassis issues is due to rust, which can seriously impair the structural rigidity of the vehicle. The inspector will check for any signs of corrosion in ‘prescribed areas’. These are areas within a 30cm radius of any safety feature or any components to which other parts being inspected – such as the brakes or suspension – are fitted. Minor signs of rust will typically just result in an advisory; however, they could cause the vehicle to fail if it’s severe.
Without your own inspection pit, it can be difficult to check every prescribed area for rust before taking your car to a test centre. That said, it’s a good idea to inspect the parts that most often corrode, such as the sills, wheel arches and around the fuel filler cap. If the vehicle has previously received an advisory over rust, it’s also recommended to get it sorted before it worsens.
6. Noise, emissions and leaks – 7.2%
All petrol, diesel and hybrid cars undergo emissions tests to make sure they don’t pollute excessive amounts of harmful gasses. To pass the test, the exhaust must not emit any smoke and the emission levels should be below the restrictions for petrol and diesel engines. The car will also fail if the engine management light is lit up on the instrument panel or, if you own a diesel car, the diesel particulate filter (DPF) has been removed or tampered with.
In addition to checking the exhaust’s emission levels, the inspector will also make sure that it doesn’t produce excessive levels of noise. Unlike new cars, which must not produce more than 72 decibels, the MOT does not limit the amount of noise a vehicle being inspected can make. Nevertheless, if the tester subjectively notices that your car is noticeably louder than other examples of that model, it could fail.
7. Impaired visibility – 6.7%
An inspector can fail your car for impaired visibility over a number of issues that could limit your view of the road – potentially resulting in an accident. This includes discolouration in the windscreen, faulty wiper motors, condensation and worn-out wiper blades.
Your car might fail its MOT if there are chips or cracks on the windscreen. Chips and cracks on a part of the windscreen that is swept by the wipers must not exceed 40mm – a limit that drops to just 10mm for the area directly in front of the steering wheel.
While any damage to the windscreen must be repaired professionally, one way you can reduce your chances of failing the MOT is by making sure the wiper blades are in good condition. Gently lift the wiper arms off the windscreen and inspect the rubber blades for signs of perishing. Worn wiper blades will typically make a scraping noise because they move across the windscreen and leave streaks of water. Replacing wiper blades is easy and only takes a few minutes.
8. Steering – 4.1%
In an MOT, the inspector will check that the steering system allows you to stay in full control of the vehicle in an emergency. A car will fail its inspection if the steering wheel is loose or misaligned, or if the mechanical steering components are excessively worn. If the car’s power steering system has failed, it will also receive a fail.
The easiest way to prevent a steering issue resulting in failure is by regularly checking the system. If your car pulls to one side when travelling on a straight and flat road, or you hear any clunks or other unusual noises get it inspected by a professional.
9. Non-component advisories – 4%
Not all issues found during an MOT are to do with the parts fitted to the car. Non-component advisories cover any miscellaneous faults, such as oil and coolant leaks or tyres protruding beyond the wheelarches. Some non-component advisories will also cover parts that are missing or difficult to access during the MOT, such as the tow hitch being removed or under-trays obscuring components underneath.
In most cases, non-component advisories aren’t serious enough to prevent a car to passing its MOT. However, if the issue is serious enough to compromise the safety of the driver and other road users, it could still fail.
10. Identification of the vehicle – 2%
All vehicles used on public roads must be fitted with a set of number plates, and the same is true for an MOT. However, in addition to making sure the front and rear plates are present, the tester will check that the registrations are in good condition – with no sign of cracks, fading and delamination – and meet the strict standards specified by the DVLA.
In particular, all number plates must feature letters in the Charles Wright 2001 font with the correct spacing and thickness, whereas the background must not have an overprinted or honeycomb-effect background. All of these issues might make it more difficult for other road users, police officers and ANPR cameras to identify the vehicle.
