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DPF Filter on Subaru Outback

We had a customer come through with a 2013 Subaru Outback that has been having issues with the Diesel Particulate Filter.

This can be an issue for most diesel engines, especially if they are used for city driving. This Subaru outback had a few years and KM's on the clock, so it was a good time for a check anyway.

After purchasing privately, the old owner mentioned there was a previous issue with the turbo and that it had been fixed by Subaru. After driving the car for only a month, the DPF light came up on the dash and then started flashing.

We know that once the diesel filter light starts flashing, it means that the vehicle had now been moved into limp mode and auto regeneration of the DPF is no longer working and it needs to be seen by a technician.

The customer took the car to another mechanic who did a force regeneration and it appeared to have fixed the fault. This mechanic also mentioned to the customer that if there were further issues, they would recommend taking it back to Subaru as they believed it was under warranty based on what the computer had told them

About a month after, the light came back on again and the customer organised to get it seen by Subaru. They were told that the filter would need replacement.

The customer knew a little bit about DPF's thanks to our website and asked if the DPF could be cleaned. They were told that they weren't sure and that they would have to send it interstate to check, an over $2000 exercise that may prove futile. Subaru had told the customer that there was no cleaning machine in Adelaide and that it would be a $5000 replacement, overall quoting $7000!

Luckily the customer had been googling the symptoms, as they saw on our website that we have a DPF cleaning machine that uses the best technologies available.

We were able to fault find the issue and found that the DPF wasn't damaged and had over 240% soot level and 1% ash level, this means we could clean it and it would work fine.

Another happy customer!

If you have had any issues with your diesel vehicle, come and see us and we can help you!

How to take care of my diesel

What is a diesel particulate filter?

A diesel particulate filter (DPF) is a filter that captures and stores exhaust soot (some refer to them as soot traps) in order to reduce emissions from diesel cars. Euro 5 exhaust emissions legislation introduced in 2009 to help lower car CO2 emissions effectively made DPFs mandatory, and since then, around one in two new cars a year have been diesel-powered.

How does a DPF work?

The diesel particulate filter works by burning off soot once it reaches a certain temperature through regeneration. There are 2 different types of regeneration methods.

Passive Regeneration
This takes place automatically and you do not get alerted to this. To get the filter trap hot enough to self-regenerate, you need to keep the vehicle running for at least 20-30 minutes at a reasonable speed - above 60kmh. This needs to be done once every full fuel tank of diesel. Stop-start driving or around city trips may not allow the exhaust to get to temperature to carry out this regeneration. If this doesn't work, the vehicle will move onto Active Regeneration
Active Regeneration
The Engine Control Unit (ECU) will read the levels of soot in the DPF. If the vehicle is not performing a passive regeneration long enough, the soot levels may rise and once it gets to approx. 45% the ECU will perform an active regeneration. This is where a small injection of diesel fuel is pushed into the engine after main combustion cycle to increase the temperature of the exhaust and to trigger the passive regeneration. You will normally see the DPF light pop up on the dashboard to let the driver know this is in process. If this process is interrupted or can't be completed for any number of reasons, the car will go into limp mode.

What is limp mode?

This security feature in vehicles causes the less important parts of the car to turn off when an issue is detected in the ECU (engine control unit). This is to protect your vehicle from any additional damage. You may experience reduced engine power, max revs may be as low as 2000 - 3000 revs, no cruise control, no heating, or air con and, if you are driving an automatic transmission, you may be locked into a low gear.

How long does a passive/ active regeneration take?

To get the filter trap hot enough to self-clean/ regenerate running for at least 15 - 20 minutes and it then takes another 10 - 15 minutes to burn the soot and clean the filter.

How should I drive my car to ensure the regeneration happens?

If your everyday use of your car does not involve a regular drive of 20 - 30 minutes, you need to make a special trip to help clear your DPF and allow active regeneration/ cleaning.

So, one trip per full tank of diesel, your car should be driven for 20 - 30 minutes at a constant speed/ highway above 60kmh to enable active regeneration.

What about my diesel fuel?

We will always recommend using premium diesel fuel as this will help your engine run smoother and cleaner. This means that your vehicle may have improved performance and will ensure soot deposits are kept low.

Never drive on empty!

When you let your diesel engine run on empty, air may go through to your injector pumps which means they will no longer perform. If that happens, your vehicle may shut down and will not restart until the air is removed. To avoid this and the problems that can come with it, we recommend filling up your tank at about the 1/4 tank mark just in case.