Diesel particulate filters - the complete guide

Diesel engines are more efficient than their petrol counterparts, and the modern turbodiesel engine provides muscle with economy and refinement – so it's no wonder there's been a move away from petrol and towards diesel-powered cars in recent years.

The key downside is that diesel cars cost more to make (and hence more to buy) than their petrol equivalents, which is why they don't make sense for many low-mileage drivers. There's another reason though, why low-mileage drivers are best buying petrol instead of diesel, and that's the diesel particulate filter (DPF). 

A DPF needs to get up to temperature to work properly, which means regular high-speed runs

One of the characteristics of diesel engines is that they emit soot particles, which hang in the air and lead to breathing difficulties – and cancer. Suddenly the diesel engine isn't looking so attractive, is it?

However, a diesel car's exhaust emissions can be cleaned up, to get rid of these particles, which is where the diesel particulate filter comes in.

The DPF traps the soot then burns it off at very high temperatures, to help improve air quality. The problem for low-mileage drivers is that a DPF needs to get up to temperature to work properly, which means regular high-speed runs. Without these the filter gets clogged up with soot particles and it can lead to major issues and costs; replacing a failed DPF can easily cost over £1000.

So if you're looking at buying a newish diesel car, and you don't drive many miles, check whether or not it has a DPF. Because if it does, you will probably be much better off buying a petrol-engined car instead.

It’s a fact

Because of the high cost of replacing a DPF, some companies offer a service whereby it’s cut out altogether

While this is good for your pocket, it’s not much good for the environment, which is why from Fenruary 2014 your car would fail the MoT on its exhaust emissions, if it came out of the factory with a DPF, which has since been removed. So if you’re buying a second-hand diesel-powered car that was made after September 2009, make sure it’ll pass an MoT.

This isn’t the date from which DPFs became mandatory, as they’re not actually a legal necessity as such. But car makers have had to fit a DPF to pass the strict emissions laws introduced in September 2009.