The measures will introduce new failure and defect categories, with faults labelled, ‘Dangerous’, ‘Major’ or ‘Minor’.
Any vehicle receiving a dangerous or major fault, will automatically fail, while a vehicle given a minor fault will still pass the test, with a record of the fault being noted on their certificate.
The new categories are being introduced on May 20, 2018 as part of a European Union directive, known as the EU Roadworthiness Package.
But according to RAC spokesman Simon Williams the classifications leave the seriousness of car defects open to interpretation by testers, creating “the potential for confusion”.
Mr Williams said: “While on the surface this change, which is part of an EU Directive due to come into force in May, seems like a sensible move we fear many motorists could end up being confused by the new categories which give an indication as to the seriousness of vehicle defects identified in an MOT test.
He adds that rather than creating a “black and white” situation over failures, the new system leaves faults open to interpretation which may cause inconsistencies from one test centre to another.
Among the changes, the Driver and Vehicle Standards Agency (DVSA) will also introduce new criteria for steering mechanisms.
Under the guidelines a steering box leaking oil would get a minor fault, however, the scale of the drip would be open to interpretation by the tester. If deemed bad enough, the drip could warrant a major and fail.
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Mr Williams says: “We do not want to see a lowering of MOT standards and a reduction in the number of vehicles failing the test compared to current levels.
“We understand the Government has little choice in the matter, but gut instinct says if the system isn’t broken, why mess with it. But if a car is broken, fix it.”
Cars will also face stricter emissions testing under the new rules, with limits for diesel cars being lowered. Any vehicle with a diesel particulate filter (DPF) will be issued with a major fault if it is found to emit a “visible smoke of any colour”.
The MOT will also include checks to see if the DPF has been tampered with or removed. If it has, testers must refuse to check the vehicle unless the owner can prove there were “legitimate reasons” for doing so, such as cleaning.
In keeping with previous MOT rules, any car missing its DPF altogether will be rejected.
Read: Will new Government MOT proposals lead to more unroadworthy vehicles across the UK?