Exhaust systems – All you need to know about Diesel Particulate Filters (DPF)
Your vehicle’s exhaust system has four main functions: to control noise, to direct exhaust fumes away from passengers, to enhance engine performance, and to improve fuel consumption. If you drive a Diesel vehicle manufactured after 2009 then it will be fitted with a DPF. You may not know what this is or how best to maintain its health.
For this reason, the team has compiled this handy FAQ checklist with all you need to know about your DPF, how to avoid problems to when to revert to a garage for a DPF clean.
What is a DPF?
In a bid to help reduce harmful exhaust emissions in diesel vehicles, car manufacturers introduced DPFs to help capture and store the excess exhaust soot.
As exhaust gases pass through the filter, fine particles are trapped in the porous walls, preventing them from being released into the air. Over time, the filter undergoes a process called “regeneration” This process is where high temperatures burn off the accumulated soot and convert it into ash which in turn helps keep the DPF functioning optimally.
These filters however have a finite capacity, which means that they can be prone to blockages. Regular maintenance is therefore necessary to prevent clogging, ensure engine performance, and reduce the chances of more costly repair work.
How do I know if my DPF it blocked or faulty?
Your dashboard will usually alert you to the signs of an issue with your DPF. You will see an orange warning light that looks like a piped box with dots in the middle. This symbol can however vary from one manufacturer to the next so revert to your handbook for more information. It also pays to familiarise yourself with other warning lights so you know if and when it is best to revert to a professional.
Can I drive with a DPF warning light on?
Generally speaking, you can drive with the DPF warning light on for a short distance or a few miles without this being an issue. and you If this light stays on and you drive for an extended period however this can cause significant and expensive damage to the engine. If you see this red warning light show up on your dashboard however, this is a sign that there is a critical issue with your vehicle and to stop driving.
What are the main causes of a clogged or faulty DPF?
There are some common causes for the regeneration not to work and for your DPF to become blocked:
- Regular short journeys at low speeds – This can mean that the DPF does not reach the right temperature to regenerate
- Not keeping up to date with your service plan – Issues would be picked up at these vital health checks
- Using the wrong type of oil – Some oils that are not specific to diesel engines can actually clog up filters
- Failed sensors relating to the DPF that fail to register that it is clogged or to trigger an engine management light (EML)
Can a blocked DPF result in an MOT Failure?
The short answer is YES. With the reduction of emissions high on government agendas, a diesel particulate filter has been part of the MOT test since 2014.
During this annual safety check, your MOT tester will be testing for excessive emissions and a blocked DPF can directly result in higher levels of harmful pollutants being released into the atmosphere through the exhaust system. It will also fail if this has been removed.
What is the best way to maintain the health of Diesel Particulate Filter?
The best way to maintain the health of your DPF is to ensure that is it able to regenerate once it is full of soot (and the light comes on)
There are two main ways to regen your DPF – Active and Passive
Passive DPF regeneration
As we previously explained, short journeys do not facilitate the optimal temperature for the DPF to clear itself through the regeneration cycle. It is recommended to regularly run your vehicle on a motorway or an A road at speed for 30 – 50 mins to allow this regeneration process to happen.
Active DPF regeneration
Active regeneration is a more controlled process that is started by the engine control unit otherwise known as the ECU. Through sensors, the ECU monitors the exhaust gas temperature, pressure, and flow rate to determine when active regeneration is required. If it is, extra fuel is sent to the exhaust, so that its temperature can be raised to burn off the excess soot that is blocking your DPF.
There are some signs that active regeneration is happening:
- Engine note change
- Cooling fans running
- A slight increase in fuel consumption
- Increased idle speed
- Deactivation of automatic Stop/Start
- A hot, acrid smell from the exhaust
What happens is the DPF is still blocked?
If the warning light remains on or turns red or your vehicle goes into limp mode, revert to your chosen garage at the nearest opportunity or a DPF Flush / Clean. What is in reality an inexpensive repair and quick fix, could result in larger financial costs or more serious damage to your diesel-powered vehicle if you fail to get it checked out.
How much does a new DPF cost?
Unfortunately, the price of a new DPF is expensive. Depending on the age of the vehicle a replacement DPF could be more than the value of the car. For this reason, we highly recommend regular maintenance and servicing to ensure the optimal health and condition of your diesel vehicle.
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