What you need to know about Diesel Particulate Filters (DPF)

Drive a diesel car? 

Chances are it has a DPF installed yet you probably won’t even know about it. That is until you see a warning lamp on your dashboard by which point you may have a costly problem!  Fear not, diesel driver, we've tried to explain the main information you need to know about DPFs, what they do, what can go wrong with them, and what you can do to avoid seeing one of these warning lights.

A DIESEL PARTICULATE FILTER (DPF) 

Diesel Particulate Filters are fitted to some diesel vehicles manufactured after 2008 and all diesel-engined vehicles registered from 2011 onwards. Diesel particulate filters are necessary to reduce the amount of harmful particles released from diesel vehicles.

Although particulate filters are very effective in reducing the amount of particulates emitted from diesel vehicles, most filters need to burn the trapped particulates off fairly regularly, referred to as ‘regeneration’.

This usually requires the vehicle to be driven at over 50mph for a short period of time. The information below will hopefully help you decide whether vehicles using particulate filters are suitable for you.

WHAT IF I ONLY DRIVE SHORT JOURNEYS? 

If the vehicle is only driven for short journeys, or at low speed, then it may not be possible for regeneration to occur. In this situation, the below warning lights will be illuminated on your dashboard. Please refer to your Owner’s Manual for further information. After seeing these warning lights you need to drive, as soon as possible, above 40mph until the light goes out. This can take up to 30 minutes depending on the amount of soot collected in the filter.

DON’T IGNORE A WARNING LIGHT

If you continue to drive at low speeds the exhaust gas temperatures cannot rise, so regeneration cannot occur. In this instance, a combination of warning lights will be illuminated on your dashboard. In this case, you will have no option but to take the vehicle to a garage for 'forced' regeneration in order to protect the engine and DPF Filter. 

The vehicle will require ‘SERVICE REGENERATION’ which can only be carried out by a workshop equipped with specialist diagnostic equipment. It may also require the oil and filter to be replaced. Be aware that as ‘SERVICE REGENERATION’ is not a manufacturing fault, the cost will NOT be covered under warranty.    

*The cost of replacing a DPF filter can be significant depending on the car you own*

HOW DO I KNOW WHEN MY CAR IS REGENERATING?

Active regeneration will be initiated every 300 miles or so depending on how you use your car and will take around 5 to 10 minutes to complete. But this will be a problem if your journeys are too short to allow the regeneration to finish. 

During active regeneration you may notice:

  • Cooling fans running
  • Faster engine idle speed
  • Automatic Stop/Start not working
  • Increased fuel consumption
  • A hot, acrid smell from the exhaust
  • Differing engine sounds

WHAT CAN I DO TO PROLONG THE CYCLE OF A DPF?

DPF’s are in fact designed to last in excess of 100,000 miles but if the vehicle is operated correctly, many will far exceed this mileage. Below are a few simple steps you can take to ensure you achieve the maximum lifespan from yours.

Read your handbook 

Find the manufacturer's recommended procedures for active regeneration and make sure you take a journey which meets all of the criteria (usually at least every 5,000 miles or 2 months - whichever occurs soonest).

REDUCE IDLING

Even at low engine speeds particulates are emitted by your engine, so keeping your engine ticking over when you're parked or not moving can clog your filter quicker, because DPF regeneration cannot occur at idle.

Ensure the correct oil is used 

DPFs require the use of specific 'low SAPS' (Sulphated Ash, Phosphorous, Sulphur) engine oils to help reduce the clogging of the filter.  Be sure to check the label for either "low SAPS" or "suitable for vehicles with DPF" before topping-up your engine oil and always remind your garage that your vehicle has a DPF and must have the correct oil, when booking in for a service. 

Regular servicing 

A problem with the fuel, air intake or Exhaust Gas Recirculation (EGR) system could increase particulate loading, as will any internal oil leaks (e.g. turbo bearing seals, piston rings) so it's important to have your car checked as per the manufacturer's recommendations.

If you are choosing a new vehicle and plan to use it mainly for town-based, stop/start driving then it is worth considering if a petrol, petrol hybrid, electric or alternatively fuelled vehicle may be more suitable for your needs. 

Take the Suzuki Vitara S for example or our New Nissan Micra or the electric New Nissan Leaf.

If a diesel is your vehicle of choice then giving consideration to the suggestions above should help reduce any unnecessary down time or costly repairs.