The diesel particulate filter light will show up on your dashboard when your car is at risk of going into limp mode due to soot from the exhaust reaching high levels. Modern diesel car engines include a particulate filter in the exhaust to combat emissions. It is designed to catch bigger soot particles that come from the exhaust.
Why is My Diesel Particulate Filter Warning Light On?
Like all filters, the diesel particulate filter can clog up. This can eventually restrict the airflow and reduce your car’s performance. As a result of this, manufacturers have also come up with several ways to regenerate the filter by raising the exhaust temperature to burn the soot and turn it into ash. When this system is not working, the diesel particulate filter warning light will turn on.
What is the Diesel Particulate Filter Warning Light?
As you drive, the computer in the car will constantly monitor the soot levels inside the filter to determine when the process of active generation is necessary. This occurs when the car doesn’t frequently reach high enough speeds for the exhaust to be hot enough to burn the soot. Instead, it burns extra fuel to raise the temperature at a lower speed, which will achieve the desired result. When you see the warning light, you should take the car to a higher-speed road and drive it for around ten minutes at a speed over forty MPH to get the temperature levels in the exhaust high enough to regenerate the filter.
What Does it Mean When the Diesel Particulate Filter Warning Light is Flashing?
Some diesel cars show a flashing light. Most of the time this will mean the same thing as a stationary light. You will need to regenerate the diesel particulate filter by driving for around ten to fifteen minutes at a certain level of revs, which burns off the particulate that has accumulated. Refer to your owner’s manual to find out more about how long you should drive your car, and the engine revs you should maintain to achieve this. The light should stop flashing and be switched off once regeneration has been successful.
How Does the Diesel Particulate Filter Warning Light Work?
This warning light is in place to let drivers know that their diesel car needs to be driven at a higher speed. This raises the temperature of the exhaust, turning soot into ash in a process known as regeneration.
What are the Common Reasons the Diesel Particulate Filter Warning Light Will Come On?
This warning light will usually show up on the dashboard for one main reason; the car needs to regenerate, which involves burning the soot to ash which is achieved by heating the temperature. This is done by traveling at high enough speeds. The light will also remain on if the car goes into limp mode, which occurs when the soot is not burned to ash and is usually a final attempt to save the filter by limiting the top speeds. This can also lead to other warning lights coming on and might result in you having to take your car to a professional for forced regeneration.
Is it Dangerous to Drive with the Diesel Particulate Filter Warning Light On?
You should try and drive at higher speeds when safe to do so if you see this warning light come on in your car. If you ignore the light, the soot will continue to build up in the exhaust filter. Eventually, the car’s computer will switch on ‘limp’ mode, which is in place to try and prevent further damage. This limits the car’s top speed to limit the soot that is being sent through the filter and is usually a last resort solution to save the filter. If this occurs, you will need to take your car to a professional who will be able to run a forced regeneration program. Waiting too long in limp mode can lead to needing a filter replacement, which could end up costing you more than your car is worth.
How Much Does It Cost to Fix the Diesel Particulate Filter Warning Light?
The cost of fixing this light can vary from free to quite expensive depending on how long you leave it. Usually, driving on the motorway at higher speeds for around ten minutes will raise the temperature sufficiently to burn the soot to ash, which should switch the light off. However, if your car goes into limp mode and you wait too long, you may need to have the filter replaced which can be a costly repair.
A new diesel particulate filter can cost between £1000 and £3500 depending on the make, model, and age of your car. And as your car ages, the cost of a replacement filter could even be more than the actual value of your car itself. If you need to replace a diesel particulate filter, it’s important to be careful where you purchase it from. Although there are suppliers of these filters that charge less than the manufacturer, they need to have the correct Type of Approval otherwise this could end up costing you even more in repairs in the long run.
Book a diagnostic for your car if you’ve noticed this light is on and if driving at a higher speed does not fix the problem. If forced regeneration is required after your car goes into limp mode, this will usually cost around £100.
Will the Car Fail its MOT if the Diesel Particulate Filter Warning Light is On?
A diesel particulate filter check has been included in an MOT test on diesel cars since 2014. The car will automatically fail the MOT if the filter has been removed from the exhaust. It is also illegal to remove the diesel particulate filter, and you can be fined up to £1000 for doing so. Since there shouldn’t be any dashboard warning lights on during the MOT, having the diesel particulate filter warning light on might also cause your car to fail.
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