Diesel particulate filters: why it’s illegal to use a car that’s had its DPF removed

Diesel particulate filters: why it's illegal to use a car that's had a DPF removed

Sophisticated filters that prevent harmful emissions from diesel engines entering the atmosphere are being removed by thousands of drivers.

Despite it being against the law for a car to be driven without its diesel particular filter (DPF) in place, an investigation by BBC 5 Live revealed that nearly 2000 drivers had been caught doing just that.

And the figure is believed to be the tip of the iceberg. In an undercover investigation, BBC reporters took a car with no DPF to three MOT test centres. At each one, testers failed to spot that the filter had been removed.

Read on to find out why drivers shouldn’t remove their car’s DPF.

Removing a diesel particulate filter risks a £1000 fine

It is an offence under the Road Vehicles (construction and use) Regulations to use a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet. Taking out the DPF does exactly this.

As a result, car drivers can be hit with a £1000 fine for driving a car without its DPF. For light goods vehicles, the fine rises to £2500. However, there is a legal loophole. Bizarrely, it is not an offence for a garage to remove the filter in the first place.

The MOT rules for diesel particulate filters

The MOT rules for diesel particulate filters

In February 2014, the Department for Transport introduced new rules around diesel particulate filters. These were intended to prevent DPFs being removed.

As part of the MOT, testers are required to inspect the exhaust system and check for the presence of a DPF. If one is missing but was fitted when the car was built, the car must fail its MOT.

How do cars pass the MOT without a DPF?

How do cars pass the MOT without a DPF?

Cars are subjected to what’s called the MOT visible smoke emissions test. It’s really only designed to identify vehicles that are in a very poor state of repair. Because of this, says the Department for Transport, a vehicle might still pass this test while emitting illegal and harmful levels of fine exhaust particulate matter.

Why shouldn’t DPFs be removed?

A diesel particulate filter is intended to reduce the levels of soot, known as particulate matter, from an engine by as much as 80 per cent. They are commonly fitted to diesel-powered cars made from 2000 or later, and help vehicles meet European emissions standards. Removing them means more of these harmful pollutants are released into the air.

Frank Kelly, professor of environmental health at Kings College London, told the BBC: “A car with a DPF removed has a particulate count 20 times higher than one with it.” Kelly claims that problems such as lung cancer, heart attacks, strokes, Parkinson’s and Alzheimer’s can be attributed to breathing in harmful particulates.

Why do people remove a particulate filter?

Drivers take DPFs off their car because they often go wrong. The filters don’t respond well to short journeys and stop-start traffic and can clog up. Replacing one is expensive – sometimes costing more than £1000. However, DPFs can be cleaned. See our guide to how they work and how much they cost to replace for more information.

How many drivers remove a DPF?

The DVSA says 1800 cars have been caught with a DPF removed, since 2014. However the investigation by BBC 5 Live, that saw three garages fail to spot when a DPF was missing, suggests it is easy for drivers to avoid detection.

Mary Creagh, Labour MP and chairwoman of the Environmental Audit Committee, called on tougher MOT testing procedures: “I’m concerned there could be tens of thousands of cars on the road which have had the DPF removed. The government should tighten MOT tests and close the legal loophole that allows garages to remove them and cheat the public out of clean air.”

How the MOT will change

A spokesman for the Driver and Vehicle Standards Agency (DVSA) said it is making further changes to the MOT manual and to the diesel emissions limits (for modern vehicles), in May 2018: “These will make the test more robust and better able to detect where emissions control equipment has been tampered with.”


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James Mills

James is a motoring journalist and former magazine editor at BBC Top Gear and Auto Express. He has scooped, reported on and reviewed most new cars of the past 20 years, and currently contributes to the Driving section of The Sunday Times.

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