What is DPF and How to Replace it

Why is my DPF light on? 

Modern diesel car owners may find themselves asking this very question, as it is a common issue. DPF stands for Diesel Particulate Filter, and as it implies, removes harmful particulates from diesel engines’ exhaust gasses. 

Controlling harmful exhaust gasses are regulated by global standards that every car manufacturer must adhere to. Most modern diesel cars must follow Euro 3, 4 or 5 standards that regulate the amount of toxic exhaust gasses and particulates that can be released into the atmosphere. These standards are very stringent and are enforced by law, where car manufactures receive massive fines if their vehicles are found to be non-compliant. These rules determine the amount of nitrogen oxides, carbon monoxide, hydrocarbons and particulate materials that can be released into the atmosphere.  

Particulate materials are solid carbon cores that absorb and contain harmful chemicals such as sulphates, nitrates, as well as metallic trace elements. Although often visible to the naked eye as a plume of black exhaust smoke, particulate matter is fine enough to enter deeply into human beings’ lungs. Short term effects are coughing, nausea and irritated eyes. Prolonged exposure can cause breathing difficulties and even asthma. 

To meet the strict emissions standards, modern diesel cars have a diesel particulate filter (DPF) that traps and burns up particulates in the exhaust gas. This results in cleaner emissions and more environmentally-friendly vehicles. The DPF traps particulate matter such as soot and burns them up over time using a thermal chemical process. The filters inside are made of expensive rare metals, and can be quite costly to replace with a new one from the dealership. To make it last, carmakers have made it regenerative, renewing its soot trapping properties through three different processes; passive, active and forced. 

Passive regeneration occurs during normal usage of the vehicle. The DPF is designed to oxidise soot via normal exhaust temperatures and generated nitrogen dioxide in the exhaust gas. Once it’s heated up enough, the DPF burns away the soot and can now continue to function. 

When a diesel car has been travelling very short distances, the soot builds up without the DPF reaching the required temperature to start passive regeneration. When the build-up of soot reaches 45% of the DPF’s total capacity, the engine will begin to use active regeneration by making the exhaust gasses hotter. This heats up the DPF quicker to burn off the soot. In some cars, the DPF light turns on when active regeneration is triggered. To help the process along, the car should be driven for at least 15 minutes, at speeds higher than 80kph, until the light turns itself off. 

However, if the soot build up is too high and the DPF light stays on, you may have to take the car to a mechanic to perform a forced regeneration.  Forced regeneration is done via specialist equipment that forces the car’s exhaust gasses to be extremely hot to burn up the collected soot. This is usually done in an open area so that the exhaust fumes can dissipate. It can take anywhere from 30 minutes to an hour. 

Like all filters, eventually the DPF will clog up and require replacement after many regeneration cycles. This is when the DPF light comes on and stays on. Diagnosing what is wrong with the DPF requires an experienced mechanic who knows what he is looking at. Quite simply, the DPF may have issues due to a problem with the engine, or it has merely reached the end of its lifespan. That would mean the DPF will have to be replaced. We sometimes hear of consumers suggesting that its best to bypass the DPF altogether as a cheap fix for the issue. However, this is punishable by the relevant environmental authorities in your state, with fines ranging from $300 all the way to $40,000 for a business.