A tougher and updated MOT has come into force in Britain to improve air quality and make roads safer.
Diesel cars are now subjected to tighter smoke limits, while new fail categories state when a vehicle should not be driven until a dangerous defect is repaired.
A number of components and functions will be tested for the first time under the refreshed regulations.
Gareth Llewellyn, chief executive of the Driver and Vehicle Standards Agency (DVSA), said: “DVSA’s priority is to help you keep your vehicle safe to drive.
“You can start to look forward to cleaner, safer vehicles, with greater clarity on any defects identified by the tester.
“A properly maintained vehicle should have no problem passing the new MOT.”
The new rules could lead to expensive bills for people who have previously taken their cars to unscrupulous garages where DPFs have been removed because they are costly to replace when faulty.
New DPFs often cost more than £1,000, which is more than the value of many cars on the road.
Among the checks being carried out for the first time under the new regime are:
- if tyres are obviously underinflated
- for fluid leaks posing an environmental risk
- reverse lights on vehicles first used from September 2009
Motoring groups have expressed concern that many drivers are confused or unaware of the new test.
Nick Reid, head of automotive technology at Green Flag, said: “The majority of drivers are going to get caught out and potentially face fines.
“We are urging drivers to read up on the new rules and ensure that they book MOTs in early.”
Some 49% of 1,866 drivers questioned by the RAC mistakenly believe vehicles found to have a “minor” fault will fail the test.
Motorists can be fined up to £1,000 for driving a vehicle without a valid MOT.
Vehicles must undergo the test on the third anniversary of their registration and every 12 months if they are over three years old.
A number of vehicle parts are checked during MOTs to ensure they meet legal standards, such as lights, seatbelts, tyres and brakes.
Twenty-eight people were killed and 413 were seriously injured in accidents on Britain’s roads in 2016 when a vehicle defect was a contributory factor.