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Diagnostics & EmissionsWhat Is Checked in an MOT Test? The Class 4 Checklist
8 July 2026 · 7 min read
What the MOT is — and is not
A Class 4 MOT is the annual roadworthiness and emissions test required for most cars and small vans. It is a legal check that your vehicle meets the minimum safety and environmental standards set by the DVSA on the day of the test. It is not a service, and it does not check the condition of the engine, clutch, or gearbox — those are covered by servicing, not the MOT.
Understanding that distinction matters, because a car can pass its MOT and still be due a service, or need work that the MOT does not assess. Many drivers book an MOT and a service together so both the legal check and the mechanical health of the car are covered in one visit.
The main areas a tester checks
The tester works through a defined checklist covering the brakes, tyres and wheels, steering and suspension, lights, mirrors, wipers and washers, the horn, the exhaust and emissions, the seatbelts, the body and structure, and the fuel system. Brakes are tested for balance and efficiency on a rolling road, and emissions are measured against the limit for your engine type and age.
Newer requirements also cover items such as the condition of the DPF on diagnostics, the correct operation of tyre pressure monitoring, and daytime running lights on cars fitted with them. The tester does not dismantle anything — the check is visual and functional, based on what can be seen and measured without removing components.
Fails, advisories, and the difference
A fault is recorded as a Dangerous, Major, or Minor defect. Dangerous and Major defects mean the car fails and must not be driven on the road until the fault is repaired. A Minor defect means the car passes but the issue should be monitored and repaired soon.
An advisory is different again — it is the tester noting something that is wearing but still within legal limits, such as brake pads getting low or a tyre approaching the tread limit. Advisories are your early warning system: acting on them before your next test usually turns a future fail into a cheaper, planned repair.
Give your car the best chance of a pass
A large share of MOT failures come down to simple things a driver can check: blown bulbs, worn wiper blades, low washer fluid, tyres below the 1.6mm tread limit, and number plates that are dirty or damaged. Walking round the car and checking the lights and tyres the week before your test catches many of these.
At Urban Autohaus we carry out Class 4 and Class 7 MOTs in West Bromwich, explain every advisory in plain English, and offer a free retest when repairs are carried out with us. Call 07498 392333 or book online — we are on Cornwallis Road, West Bromwich, B70 9BY.