So you want to DIY clean your own DPF filter? Here’s what you need to know before you start.
What is a DPF?
DPF is short for ‘diesel particulate filter’. Like all filters, the DPF’s job is to let air flow through while screening out dirty particles. If you are looking underneath a diesel car, truck or van, the DPF device is an extra ‘box’ part of the exhaust system.
After exhaust fumes exit the engine, the DPF ccollects soot / diesel particulate and other nasty particles on the way down the exhaust pipe. This prevents them from being released into the environment. A diesel particulate filter can remove 85%+ of the dirt from the exhaust, reducing harmful emissions.
In many countries, the addition of a DPF to diesel vehicle exhaust systems became industry standard around 2009 onwards as car manufacturers came in line with new emissions laws.
The DPF physically captures the soot and ash particles in a net or mesh like structure within the filter, just like a cigarette filter collects tar. It is a relatively simple technology, nothing fancy. Just a filter in a holder. However the materials used to MAKE the filter itself ARE fancy, hi-tech lab materials that you can’t just make anywhere. They allow air to pass through, but the holes have to be small enough to trap the pollution.
And here lies the problem; those tiny space-age material holes clog up over time, which means no air can flow through them, the whole system starts to back up down the line and your previously healthy vehicle will start being affected in lots of noticeable ways such as power loss, bad efficiency and other problems. Long term, driving around with a clogged DPF will wreck your engine. But unlike other types of filters on a vehicle, the expensive materials used to make it mean you can’t just throw the DPF away and buy a new one without paying a hefty price. They are not cheap.
Also, the filter is welded into a steel box, making it hard to get to. This is a job that requires specialist tools and a car hoist, not something you want to do flat on your back in a driveway.
So how do we solve the problem of a clogged DPF? Well, there are a couple of different things.
Difference between REGENERATION and CLEANING your DPF
First of all, because designers know that the DPF will clog, they have already built in a system that can help. Sensors measuring the pressure and temperature in the exhaust system tell the ECU (Electronic Control Unit – your vehicle’s onboard computer) that the DPF is clogging. The ECU then changes the way the engine operates to make the exhaust run red hot and burn off the particles into tiny ash that then blows out of the unit.
It will usually do this when the vehicle is running at speed on the motorway, so that the extra heat is controlled with the airflow of running at speed. It may do this several times. This process is called REGENERATION, and it may do this several times.
The dashboard usually displays a symbol like this to tell you the process is happening.
But if you are not driving for long enough, the system may not get enough time to cycle properly. Do this enough times, and it will register as a fault and the light will stay on. At this point, you need to do something about it.
DPF REGENERATION / CLEANING
Two different types of DPF regeneration are commonly used – ACTIVE and PASSIVE.
Either type need to meet conditions for the regeneration to start, usually a combination of engine temperature, speed and RPM. The engine needs to have reached normal operating temperature, travelling at more than 40MPH and the RPM (revs) of your engine is above 2500 RPM. More blockage means more time cycling.
DPF Regen Conditions
- Engine at normal operating temperature
- At least 40MPH
- At least 2500RPM
- Fingers crossed!
The different types of regeneration.
ACTIVE REGENERATION (Becoming the usual standard on cars)
ECU triggers a post combustion fuel injection (fuel goes into the DPF instead of burning). This increases the temperature, cooking the soot and particles built up in the filter. Obviously this technique can cause higher than normal fuel usage.
PASSIVE REGENERATION (usually on trucks)
Passive DPF regeneration happens automatically on motorway-type runs when the exhaust temperature is high. Many car manufacturers have changed to active regeneration as motorists in cities do not typically drive long distances at motorway speeds. Passive regeneration often also requires a DPF additive (see below).
FORCED REGENERATION (Halfway fix in a workshop)
Forced regeneration is a way of cleaning the DPF using a maintenance process which has been built in by the vehicle manufacturer. This process can only be started by either a main dealer / mechanic with the right tools and access to the vehicles computer management systems.
It involves creating a DPF clean cycle in the workshop which runs the car at a high RPM for a considerable period of time. The ECU ensures that this cycle heats up the DPF filter to an extreme temperature, burning the contents of the filter.
In some cases the ECU injects fuel into the post combustion process to achieve these temperatures. In most cases the engine oil will need to be changed as the vehicle will literally “cook” the lubricant.
Machine Cleaning the DPF
This involves removing the unit and hooking it to a large specialised ‘vacuum’ type machine that uses ultrasound and chemicals to breakdown and blast out the DPF. The unit will need to be removed from the vehicle by someone who knows what they are doing and then sent to a company that has one of the machines for cleaning. The total cost of removal, courier, cleaning and re-fitting is usually still well below the cost of a replacement DPF.
DIY DPF Cleaning
If you have already read the first section, then you will understand the steps you can take to help clean the DPF using the vehicles, inbuilt system.
If you missed that section, click here.
If you now want to know how to physically clean the DPF yourself, read below.
WHAT IS A DPF ADDITIVE?
Some manufactures use a DPF additive which is automatically added to the fuel. This additive increases the chance of successful DPF regeneration.
The additive allows soot and ash to “burn” at a much lower temperature than during an active regeneration. The additive is usually replaced during servicing as part of manufacture guidelines.
There are “over the counter” DPF additives which can be added to your fuel tank. These too claim to help reduce the temperature which soot will burn. These products have varying degrees of effectiveness, but none of them will work once the DPF has reached a blocked condition.
We do not recommend any of them.
WHY ARE DIESEL PARTICULATE FILTERS SO EXPENSIVE?
DPF filters contain a fine mesh structure that functions as a net. This net collects soot and diesel particulates, preventing release into the air. Modern DPF filters are made from various materials such as a matrix of porous ceramic material, Silicon carbide or metal fibers. Due to the materials used and complex design of the structure the filter itself can often cost upwards of a couple grand.
HOW LONG SHOULD A DPF LAST?
The lifespan of a DPF is very hard to gauge with many factors but expect a DPF for the average vehicle to last 50k kms+ from new. For the occasional city driver this maybe considerably sooner due to increased soot levels and the ability for the DPF to regenerate under normal driving conditions.
CAN I CLEAN MY DPF MYSELF WITH A PRODUCT?
The only way to effectively clean a DPF is with a specialty machine. These machines are industrial level and operated from a professional workshop. They work like a big vacuum cleaner with a chemical bath attached.
If you are in Taupo, you can bring your vehicle to our facility and, once removed, we can clean the DPF for you. If you are elsewhere in the country, you can get your DPF removed at a mechanic shop and they can send the DPF to us for cleaning, then have it returned.
WHAT SHOULD I DO WHEN I SEE THE DPF WARNING LIGHT?
Depending on the model and make of your car, the process of regenerating the filter will differ. If you don’t know how to clear the DPF then we would advise seeking advice on the vast array of owners club message boards and forums.
Failing to correctly regenerate a DPF can lead to a costly manual regeneration or in the worst case – failure of the device. See the section above for information on how regeneration takes place however we would strongly suggest that you speak to a mechanic before wasting time and fuel.
DPF WARNING LIGHT AND CHECK ENGINE / MANAGEMENT (ENGINE WARNING LIGHTS) ARE ON
With most vehicles the DPF warning light will illuminate to notify you that the unit is becoming blocked and requires regeneration. When the car meets it’s conditions for a regeneration it will attempt to burn off the built up soot using either an active or passive regeneration. If the regeneration is unable to occur or fails you may be treated to an additional light on your dash in the form of an Engine Management Light or Check Engine Light. This usually occurs when the car is beyond the point at which a normally regeneration may occurs and indicates a dealer / garage visit is in order.
When the EML / CEL appears your car may go into limp home mode. This may restrict engine power and revs, resulting in additional misery!
I HAVE A DPF, WHAT ENGINE OIL SHOULD I USE?
Always use the manufacturer approved engine oil if you have a DPF. Most manufacturers specify a low SAPS oils. Low SAPS oils are specifically designed to be low in Sulphated Ash – a by-product of diesel combustion that causes the DPF “mesh” to become be blocked. It’s also advised to ensure your oil is changed well within recommended manufacturer guidelines.
WHAT CAN CAUSE BLOCKED DPF?
Faulty / Damaged EGR Valve
It’s not just your driving habits that can cause your DPF to block. There is another little gremlin sitting under your bonnet that could be the cause of all your DPF woes… your EGR valve.
An EGR Valve is a small engine component that recirculates a portion of your exhaust gases back into the engine. This process is primarily aimed at reducing the levels of nitrous oxide (NOx) being emitted through the exhaust system.
Over time EGR valves can become blocked with the soot and carbon it is designed to recirculate, this in turn can cause the device to stick open or open for longer than it should.
A faulty EGR valve that is stuck open will increase the amount of particulates, soot and carbon to to be fed back into the engine, in turn increasing particulates produced by the engine and causing your DPF to become blocked much quicker than expected.
A faulty EGR valve will often cause an error code in the ECU and may also cause the car to idle roughly. We’d recommend having your EGR checked if you are experiencing recurring DPF regeneration or frequent DPF warning lights.
Read more about how EGR valves work and how they can affect both your DPF and engine here.
CAN I REMOVE MY DPF?
The removal of the DPF will cause the ECU error and therefore the service will most likely also include the removal of the error and associated programming from the ECU software.
IS MY DPF FILTER COVERED UNDER WARRANTY?
The DPF is seen as a consumable by many manufacturers and warranty providers. The cost of replacing or regenerating the filter is normally not covered but we would suggest seeking advice if you are experiencing DPF related issues.