Around 1.5 million vehicles fail their MOT every year in the UK for issues so simple that drivers cannot believe it when they hear the result. A bulb they did not know had blown. A washer bottle they forgot to top up. A number plate that had been quietly peeling since last winter.
I have been testing and preparing cars for MOT at our Bromley workshop for fifteen years. The failures that frustrate me most are not the mechanical ones — the worn brakes, the blocked DPF, the suspension bushes that need replacing. Those are genuine wear-and-tear issues. The ones that sting are the failures that cost £3 to prevent and £54.85 plus a retest fee to learn about.
This article is about those failures. The ten things that catch drivers out every year — not because their car is in poor condition, but because they did not know to look.
1. The Number Plate Light Nobody Ever Checks
Of all the lights on your car, the number plate light is the most commonly forgotten and among the most frequently failed. There are usually two small bulbs illuminating your rear plate. Either one failing is a major MOT defect. Walk around your car tonight with the sidelights on and check. If you cannot see a clear white glow on your rear plate, you have found a failure waiting to happen. A replacement bulb costs under £3 and takes two minutes.
2. An Empty Washer Bottle
This one surprises drivers every time they hear it. Around 1.5 million vehicles fail their MOT for simple issues including an empty windscreen washer bottle. The tester activates the washers to verify the system works. If nothing comes out, the test stops there — major defect, fail. The tester does not check why it is empty. They simply record that the washer system did not deliver fluid to the screen. Fill the bottle completely before your test. Use proper screen wash concentrate, not just water — it prevents the jets from freezing and improves the cleaning action.
3. Rear Brake Lights — The One You Cannot See From the Driver’s Seat
You can check your front lights yourself. Rear brake lights are trickier without a friend to help. Get someone to stand behind the car while you press the brake pedal firmly. Check all three brake light positions if your car has a high-level third brake light in the rear window — this is a separate bulb that fails independently of the lower ones. A car that stops perfectly and has excellent brakes can still fail its MOT test because a brake light the driver never noticed was not working.
4. Dashboard Warning Lights That Nobody Investigated
If the engine management light, ABS warning, airbag light, or brake system light is illuminated when you drive your car to the test, the test ends there. All four are major defects. Many drivers live with a dashboard warning light for weeks or months, assuming it is minor or intermittent. At the Sanu Motors workshop, we carry out a full car diagnostic check before the MOT for exactly this reason — a fault code costs far less to investigate and resolve with time to spare than after a failed test under pressure.
5. Wiper Blades With a Split in the Rubber
Run your finger along each wiper blade. You are feeling for splits, tears, sections where the rubber has begun to separate from the frame, or hardening that makes the rubber inflexible. Blades that leave smear marks or skip across the screen rather than clearing it cleanly will fail the MOT. New wiper blades cost £10 to £25 for a pair and take five minutes to fit. Most drivers replace them when they become annoying to use. The MOT tester replaces them — in the sense that your car fails — the moment they stop clearing the screen effectively.
6. The Handbrake That Almost Holds
Apply the handbrake on a gentle incline and release the footbrake. Wait. If the car moves even slightly, the handbrake efficiency is below the threshold required for an MOT pass. Handbrake cables stretch gradually over time and the deterioration is so slow that most drivers do not notice it happening. This is one of the top recorded reasons for MOT failure in DVSA data year after year. Test yours on a hill before the test date and book a brake inspection at Sanu Motors if there is any doubt.
7. A Cracked or Peeling Number Plate
Number plate defects account for around 4 percent of all MOT failures in the UK. Delamination — where water gets between the layers of the plate and causes the reflective backing to separate and bubble — is particularly common after cold and wet winters. A plate that is cracked, chipped, or peeling is a major defect regardless of whether the registration is still readable. Check both plates in daylight and replace any that show visible damage. A pair of replacement plates costs £15 to £25 from most accessory shops.
8. A Tyre With a Sidewall Bulge
Tread depth gets all the attention. Sidewall condition gets almost none. Run your hand around each tyre’s sidewall — with the engine off and handbrake on — feeling for any bulge, lump, or raised area. A sidewall bulge indicates internal structural failure and is an automatic dangerous defect at the MOT, regardless of how much tread is left. It is also a blowout risk on the road. If you find one, do not drive to the test — arrange a replacement first and have the car inspected, because the underlying cause may be an impact that also damaged a suspension component.
9. Oil Level Below Minimum
The MOT tester will not run the emissions test if the engine oil level is below the minimum mark on the dipstick — they cannot run the engine safely at the required conditions. Check the oil level on a flat surface using the dipstick, and top up with the correct specification oil if it is below the minimum mark. This check takes two minutes and costs nothing unless the oil needs topping up. Yet cars are turned away from MOT test stations for this regularly.
10. A Chip in Zone A of the Windscreen
Zone A is the 290mm-wide band directly in front of the driver, within the swept area of the wipers. Any chip or crack larger than 10mm in any direction within Zone A is a major defect — the equivalent of a crack the size of a 10p coin, positioned where the driver looks at the road. Many drivers are aware of a chip on their windscreen but have lived with it for months without measuring it or having it assessed. If it falls in Zone A and is over 10mm, it will fail. Windscreen chip repair where the chip is in a repairable location takes 30 minutes and costs £20 to £40. A new windscreen costs considerably more. Get the chip assessed before the test, not after the failure.
The Pattern in All Ten
What these ten failures have in common is not mechanical complexity — it is visibility. None of them require specialist knowledge to find. All of them are visible to any driver who takes twenty minutes to walk around their car and look carefully.
The MOT is not designed to catch you out. It is designed to confirm minimum roadworthiness standards. A car that fails for an empty washer bottle or a number plate light is not a dangerous car — it is a car whose owner did not know to look. Now you do.
If you would prefer a professional to do the looking, a pre-MOT inspection at Sanu Motors in Bromley covers every item on the test criteria in around 45 minutes. We tell you honestly what will fail, what is borderline, and what needs no attention. Booking before your test date rather than after your failure is almost always the cheaper choice.
Call 07551 021029 or visit sanumotors.com to book your MOT or pre-MOT inspection at our workshop at 76A College Road, Bromley, BR1 3PE.