Vehicle test procedures
Detailed information on what happens at each stage of a vehicle test (MOT).
When you arrive at the test centre
The link below has information on what happens when you arrive at the test centre and what you can expect.
Stage one
The vehicle examiner will take your vehicle through the MOT Test. On entering the inspection hall, the vehicle details will be checked and recorded on computer. The vehicle's exhaust emissions will be checked first.
Diesel smoke test
The smoke emitted from all diesel engined heavy goods vehicles and buses (including rigid goods vehicles, articulated goods vehicles, road construction vehicles, tower wagons, breakdown vehicles, motor tractors, mobile cranes, display vehicles, large passenger carrying vehicles, omnibuses and play buses) is assessed for its density. It is carried out by the use of an approved and calibrated smoke meter.
The engine will be accelerated up to governed speed and the density of the smoke measured.
After the third acceleration the average reading is recorded. If the reading is below 2.5m-1 for non-turbocharged engines or 3.0m-1 for turbocharged engines the vehicle will pass.
Diesel vehicles first used from 1 July 2008 to 1 January 2014 must have a reading of 1.50, and those vehicles first used on or after 1 January 2014 must have a reading of below 0.7m-1.
However if the average is higher, a further acceleration is carried out and the average of the last three readings are used, this will continue until a maximum of six accelerations have been carried out.
If the average of the fourth, fifth and sixth acceleration is higher than the right level the vehicle will not pass the test.
Also, any of the following will result in the vehicle being refused a certificate:
- exhaust emits too much smoke or vapour of any colour, to an extent likely to obscure vision
- emissions cannot be measured because a tail pipe is damaged or an accessory is fitted which prevents the insertion of the smoke meter probe
- insufficient oil in the engine or low oil pressure which could cause engine damage if engine is accelerated
- obvious signs of an engine defect such as an unusual noise or emission of smoke
- obvious signs that the governors have been tampered with or are not operating
It is important that vehicles are properly maintained (including changing of timing belts) in line with the manufacturers' recommendation and presented for test at normal working temperature.
Petrol exhaust emission
This test applies to all petrol engined cars, taxis, minibuses and ambulances with up to 12 passenger seats, and other vehicles up to and including 3,500 kg design gross weight (DGW), which are petrol (spark ignition) engined with four or more wheels.
Any of the following points will result in the vehicle being refused a certificate:
- engine is idling at a speed clearly above its normal idling speed
- engine emits dense blue or clearly visible black smoke for a continuous period of five seconds at idle
- engine emits dense blue or clearly visible black smoke during acceleration, which would obscure the view of other road users
- emissions cannot be measured because the tailpipe is damaged or an accessory is fitted which prevents insertion of the analyser probe
- exhaust gas contains one or more gases more than the required limits for the test
Under bonnet inspection
An under bonnet inspection is carried out at this stage.
Also checked at this stage:
- registration plates and vehicle identification number (VIN)
- power assisted steering
- engine transmission mounts
- mechanical brake components
- hydraulic, air and vacuum brake systems
- fuel system
- brake and steering fluids
- general condition of the vehicle
- vehicle structural integrity and construction
Additional mirrors required on heavy goods vehicles
European Directive 2007/38/EC requires trucks over 3.5 tonnes and first registered on or after 1 January 2000 to be fitted with a wide angle mirror and a close proximity mirror - both mirrors are to be fitted on the nearside of the vehicle.
These additional mirrors are needed to help drivers see other road users in the areas immediately around their vehicles to reduce the potential for collisions.
Stage two
The second stage of your vehicle MOT test starts with the headlight alignment check.
At this stage the following items will also be checked by the examiner:
- headlamps
- direction indicators
- stop lamps
- reversing lamp
- rear reflectors
- seat belts
- seats including driver's seat adjustment mechanism
- windows and windscreen
- windscreen washers and wipers
- horn
- mirrors
- hazard warning lamps
- front and rear position lamps, registration plate lamps and front and rear fog lamp
- daytime running lamps
- body condition
- doors, boot lid and bonnet
- steering column lock
- trailer tow bar and electrical connections
- general condition of vehicle
- vehicle structural integrity and construction
Headlamp alignment testing criteria
The most common type of headlamps fitted to vehicles are those known as European type headlamps which are checked for aim on the dip beam.
These headlamps have an asymmetric dipped beam pattern with a distinctive horizontal cut-off on the right, and a 15 degree wedge of light above the horizontal (the 'kick-up') towards the left.
Any of the following points will result in the vehicle being refused a certificate:
- beam pattern blurred and does not show a distinctive cut-off point
- beam 'kick-up' is to the offside, that is, the headlamp dips to the right
- image break point is not between the vertical -2.0 per cent line (blue vertical line) and the vertical 0 per cent line (black vertical line)
- headlamp centres not more than 850mm above the ground - the beam horizontal cut-off line (pitch) is not between -0.5 per cent and -2 per cent line (red lines)
- headlamp centres more than 850mm above the ground - the beam horizontal cut-off line (pitch) is not between -1.25 per cent and -2.75 per cent line (green lines)
There will be no opportunity to adjust headlamp alignment during the test. Levelling devices should be set for unladen condition, normally located on vehicle dash.
After the lights have been inspected you will be asked to leave your vehicle and open the fuel cap (this is to inspect the seal on the cap as many accidents have been caused by fuel spillages) and the car boot.
The boot should be free of luggage to allow the examiner to inspect the boot floor and body structure.
The examiner will now drive your car forward to stage three.
Stage three
The third stage of your vehicle MOT test starts with the shock absorber test.
Brake test
The examiner will take the vehicle through the break test where the wheels will be placed on rollers and the brakes applied.
Brakes testing criteria
Any one of the following points about brake performance will result in a vehicle being refused a certificate:
- low braking effort recorded from the brake on any wheel, indicating clearly that the brake is not functioning correctly
- significant braking effort recorded on road-wheels, even though the brake is not applied, indicating that a brake is binding
- evidence of severe brake grabbing or judder as the service brake (foot brake) is applied
- the service braking efforts at the road-wheels do not increase at about the same rate when the service brake pedal is applied gradually
- the service braking efforts at the road-wheels do not reduce at about the same rate when the service brake pedal is released gradually
- the out-of-balance of the service brakes on any axle, greater than 30 per cent
- the service brake efficiency is below 50 per cent (58 per cent for cars first used on or after 1 January 2012)
- the parking brake (hand brake) efficiency is below 16 per cent
When the brake test is complete the examiner will drive forward and stop in front of the hoist. They will then ask you to take a seat in the waiting area where you can watch the rest of the test being carried out. Stay here until the examiner has completed the inspection and called you forward.
Interior inspection
At this stage the driver's compartment will also be inspected, which will include:
- parking brake lever mechanism (hand brake)
- service brake control
- speedometer
- disabled driver control if applicable
- driver controls
- steering control
- vehicle warning lights including, engine management system, anti-lock braking system, electronic braking system, electronic power steering, electronic stability control, electronic park brake, brake fluid warning lamp, tyre pressure monitoring system, air bag, seat belt pre-tensioner and seat belt load limiter
- vehicle tell-tale lights including, hazard lamps, head lamp main beam, direction indicators and rear fog lamps
Stage four
The examiner will position your vehicle on the hoist for the under body inspection.
Under body inspection
An under body inspection will look at the items listed below and could include the examiner taking the vehicle for a short road test within the test centre grounds.
The following items are looked at:
- electrical wiring
- body condition
- steering system
- tyres
- road wheels and hubs
- suspension, wheel bearings and drive shafts
- shock absorbers
- oil leaks
- engine and transmission mounts
- transmission
- exhaust system including the catalytic converter
- mechanical brake components
- brake hydraulic, air and vacuum systems
- fuel system
- spare wheel and carrier
- general condition of vehicle
- vehicle structural integrity and construction
The list above of items that are checked at each stage of the inspection are not exhaustive but identifies the main items that will be inspected.
Your vehicle could be randomly selected for a re-check by centre management at the end of the test. If your vehicle is chosen it will go back through the MOT testing process as part of a quality control to make sure that standards are maintained. More information is available at the following link:
The examiner will then advise if your vehicle has passed or failed.
If your vehicle passes the MOT test, the examiner will issue you with an MOT certificate. You no longer receive a MOT disc to display on the windscreen.
The MOT certificate may list any minor defects which will have no significant effect on safety or the environment. This will allow you to address these faults in good time, to prevent them developing into more serious problems.
If your vehicle does not pass the MOT test, the examiner will give you a record sheet containing details of the faults which will have to be repaired for the retest.
You can book a retest at the first link below, at a reduced fee within 21 days of failing the full test, or else you'll have to pay the full fee again.
Where a retest is booked at the reduced fee, the test must be carried out within 60 days of the original, failed, test.