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The Institute of Advanced Motorists (IAM) has highlighted three of the most common aftermarket tweaks that can render vehicles illegal to include:
1. diesel particulate filter removal
2. fitting xenon headlights
3. reprogramming or ‘chipping’ vehicle electronic control units (ECUs)
Diesel Particulate filters (DPFs) can cause problems for some van operators who frequently stop in urban areas, mainly because the DPF doesn’t run at the optimal temperature during city centre driving, leading to the item occasionally clogging up and failing to work, followed by a lengthy repair. Some garages will offer to remove the item, but the result of these tweaks is an increase in deadly pollutants and CO2 emissions.
IAM head of technical policy Tim Shallcross said: “DPF removal has always been illegal but since 1 January 2014 has also been reason to fail an MOT. Some garages are blatantly still doing it. In short – they are selling a service that’s killing people.”
“Removing a DPF isn’t a task that can be done accidentally, as it involves reprogramming the engine management computer. Before 1 January it wouldn’t count as an MOT fail; but unscrupulous traders still offer to cut the case open from the top of the unit, remove the filter and welt it shut again – in an attempt to pull the wool over the eyes of the tester to achieve an MOT pass.
“This is disgraceful, but people are rarely prosecuted for this openly advertised service.”
Xenon headlamp conversions are also a major hazard. If headlamps do not have a self-levelling or washing function, they can dazzle oncoming traffic, potentially causing an accident.
Shallcross said: “Fitting this kind of lighting is illegal. Claiming ignorance of the law is no excuse; these lights which people choose because they look stylish could potentially have tragic consequences.”
Finally, the reprogramming of ECUs, or ‘chipping’ is another popular modification that is fraught with hazards.
Shallcross said: “No aftermarket warranty company will offer to cover a car that has been chipped. If you don’t tell you insurer it is likely to invalidate your policy.
“But if you do tell your insurer, he could refuse to cover your car at all, or could demand a hefty increase to your premium. Is it really worth it in the long run?”