New Legislation: Filtering out illegal motorists at the MOT

Mike Humble / VOSA

For some years now, catalytic converters, and more recently, diesel particulate filters (DPF) have caused many owners to remove or bypass such equipment. In the case of diesel cars, this is often done simply to save garage bills for switching off engine management warning lamps caused by the clogging up of the aforementioned DPF.

In the quest for lower emissions that itself brings the advantage of lower taxation (VED) classes, the DPF system is a vital part of the car that must function at all times in order for the car / van to reach that all important low smoke emission goal. The vehicle and operators standards agency (VOSA) have seen a rising number of DPF systems removed and are taking steps to ensure E.U compliance of exhaust emissions.

Tests for diesel cars and lorries are to be tightened up to ensure vehicles have a critical exhaust filter if one had originally been fitted as standard, Roads Minister Robert Goodwill has announced. Garages and testing stations will be required check for a diesel particulate filter (DPF) in the inspection of the exhaust system as part of the MOT test (or annual test for heavy vehicles) from February 2014.

The vehicle will automatically fail the MOT test if the filter had been fitted as standard but is found to be no longer present. The filter works by trapping solid particulate matter from exhaust gases. This type of filter has been in use for more than 20 years and helps meet European emission standards, improving air quality and health standards.

A typical DPF installation (V.A.G system shown)
A typical DPF installation (V.A.G system shown)

Some firms offer services to remove the filter, claiming it will improve the economy. But it is an offence to drive a vehicle that has been modified this way, as it will no longer meet the emissions standards the car achieved when it was approved for sale in the UK.

Roads Minister Robert Goodwill said:


I am very concerned that vehicles are being modified in a way that is clearly detrimental to people’s health and undoes the hard work car manufacturers have taken to improve emissions standards. It has become apparent the government had to intervene to clarify the position on particulate filter removal given the unacceptable negative impact on air quality.

This change to the MOT tests makes it clear – if you have this filter removed from your car it will fail the test.

The filters need to be ‘regenerated’ regularly through burning the soot to gas at a very high temperature, leaving behind a residue. If not carried out properly, regeneration can lead to a build up of soot, which can affect performance. This has led to some diesel vehicle owners opting to remove the filter, which makes their car illegal for road use.

Low mileage uses often suffer the warning light advising of a DPF problem that can simply be avoided by a relatively short high speed journey – in some cases as little as 20 minutes on a dual carriageway or motorway once a month suffices. Many of you I’m sure many would rather do this than have the dealer carry out this function and cancel the warning lamp – or in some cases complete and costly replacement of the DPF unit.

For those technically minded  CLICK HERE to read the official MOT testers guidance notes.

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