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A weird warning on your diesel dash could be your particulate filter

The job of the particulate filter, which is part of the exhaust system, is to trap and remove the black sooty particles that diesel engines emit. Ram / Handout
The job of the particulate filter, which is part of the exhaust system, is to trap and remove the black sooty particles that diesel engines emit. Ram / Handout

BRIAN TURNER

If you drive a newer diesel pickup truck or SUV, chances are it has a particulate filter. If you’re new to this type of engine, you may want to brush up on the owner’s manual section regarding how it works — specifically, how it cleans itself.

What is a particulate filter?

The particulate filter is part of the exhaust system. It looks similar to a catalytic convertor, and is usually mounted very close to the exhaust manifold. As the name suggests, its job is to trap and remove the black sooty particles that diesel engines emit. The problem is, those particles don’t go anywhere and will eventually render the filter useless — unless the filter is somehow cleaned.

How are particulate filters cleaned?

It’s the cleaning process that takes many new diesel owners off-guard. One of the most common methods is to burn the particles off — yes, burn them to ash, which can be expelled through the exhaust. Doesn’t sound very clean or environmentally friendly, does it? The burning process is euphemistically referred to as self-regeneration and involves feeding a very rich air/fuel mix into the engine. Of course, this doesn’t allow all the fuel to burn, and that’s the point. The excess fuel then ignites inside the filter, turning the particles to ash.

Vehicles that use this system will have a dash warning light to let drivers know when it’s about to happen, and when it’s in process. This is important because it usually takes a minimum of 10 to 12 litres of fuel to complete the task, and it will drastically increase the operating temperature of the exhaust. If the vehicle is idling, the cleaning may still take place but with warnings (in the owner’s manual) to make sure there are no flammable materials in close proximity to the exhaust.

The cleaning process will continue until the engine’s computer determines that things are flowing freely again. This is accomplished with pressure sensors on either end of the filter. Aborting a cleaning cycle process while it’s in process (by turning off the engine, for instance) brings the risk of plugging the filter beyond the system’s ability to self-correct. These filters aren’t cheap, running $1,500 and up — before installation.

A few words to the wise

There are plenty of fuel additives on parts store shelves claiming to assist this process, but like most fuel additives, their claims should be taken with a grain of salt. As well, since the cleaning schedule is rather unpredictable, keeping a minimum one third of a tank of fuel at all times is important. And don’t forget to read up on the process for your particular engine in the owner’s manual so you understand the instrument panel warnings when they appear. Moreover, avoid unnecessary idling as this can lead to an increase of particles in the filter. And finally, using the engine’s block heater in winter can drastically cut the amount of warm-up time to achieve heat in the cabin.

Copyright Postmedia Network Inc., 2020

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