How Diesel Particulate Filters Work
As with any filter, they ‘filter’ or trap particles, in this case harmful diesel exhaust soot particles, so they have to be emptied regularly to maintain performance. The DPF needs to be cleaned regularly, through a process called regeneration, either active, passive or forced regeneration, the accumulated soot is burnt off at high temperature (around 600°c) to leave only a residue of ash, effectively renewing or regenerating the filter, ready to take on more pollution from the engine.
Click here to watch the video of the JLM DPF Cleaner (3-step approach).
Active regeneration
The active system works off a filter load limit or sensors reading exhaust backpressure or the ‘soot load’ of the filter, activating timing adjustments to the fuel injection which in turn increases the exhaust temperature, initiating the burning of the soot and regenerating or clearing the filter. Depending on the vehicle brand, This type of DPF regeneration can also be initiated by the vehicle ECU every 400 - 600 kilometres or so depending on vehicle use and takes around 10 minutes to complete. 
- For active systems use JLM DPF Cleaner
Passive regeneration
Some manufacturers use passive regeneration. For these vehicles passive regeneration generally takes place on the motorway where exhaust temperatures are higher. This type of system can have an integrated oxidising catalytic converter located close to the engine where exhaust gases are hot enough so that passive regeneration is possible. Passive regeneration, relies on the exhaust temperature being high enough to automatically burn off, (motorway driving) and or using the ECU to alter the vehicle timing to control the process. In city driving or short trips the regeneration my not take place fully, leading to blocking of the filter. This can lead to higher fuel consumption and a visit to the mechanic for cleaning or replacement.
- For cars that have a passive regeneration use the JLM DPF Cleaner
Forced Regenerations
When your vehicle displays second stage DPF warning lights it will go in to ‘limp mode’ and should be taken to your garage or dealer to ascertain the extent of the problem.
A forced regeneration involves the garage using a computer program to run the car, initiating a regeneration of the DPF. This will also require changing the engine oil & oil filter.
Why does my Diesel Particulate Filter (DPF) block
Every vehicle type & engine combination can have differing reasons as to why the filter blocks. The rate
of particulates generated by the engine, the quality of the fuel, quality of the or oil, driving style, even the
location of the DPF in the exhaust system can all contribute to the filter blocking or not regenerating fully.
Generally, the problems arise in around town stop start driving where the regeneration process might not complete. A warning light will illuminate or a message indicating the DPF is full displays on the dash. If you continue to drive in the same manner, the soot build up will increase until other warning lights illuminate and the vehicle will go into ‘limp’ mode, where driving speed is restricted.
How much does it cost to replace a diesel particulate filter?
This warning stage will now involve a visit to the mechanic to carry out a forced regeneration on the filter, where filters that cannot be regenerated will then cost you between $1000 - $1500 to replace the filter.
What are the symptoms of a blocked diesel particulate filter?
- Use low ash engine oil: Not using the correct oil specified for your engine can significantly add to the soot buildup in the DPF.
- 100% Diesel Bio Fuel: Using these Bio Fuels can also contribute to extra soot build up loading in your DPF as the Bio Fuel may not burn as ‘clean’ (produce more particulates) as your regular Diesel fuel.
- City Cycle driving: We don’t all use our cars in the same way, if you only use your car around town you may experience a faster buildup of soot in your DPF as the regeneration process may not complete in short city or around town driving.
- Temperature: The DPF relies on temperature to carry out a filter regeneration, at around 600c, so a lot of short trips, low speed driving will not provide the exhaust system with a high enough temperature to begin or complete a regeneration, so the filter can block up faster.
- High Kilometre vehicles: As these vehicles with DPF systems age they will start to show that filter regeneration is harder to complete. Like any part on the car they do wear out and can no longer be repaired.
What do I do if my PDF warning is on
Follow vehicle manufacturer’s handbook on procedure to unblock the DPF. It should be possible to start a complete regeneration and clear the warning light simply by driving for 20 minutes or so at speeds greater than 60klm per hour.
At this point you should also add a single 100ml dose of JLM DPF Cleaner to a full tank of fuel, then drive as normal. This should clear the warning light within the first few hundred kilometres -depending on how blocked the filter is.
Add a second dose with the next tank of fuel if necessary. If you ignore the light and keep driving in a relatively slow, stop/start pattern soot loading will continue to build up until around 75% filter capacity, then you can expect to see other dashboard warning lights illuminate too. At this point driving at speed alone will not clear the blockage and the car will have to go to a dealer for evaluation and possibly a forced regeneration.
We see more evidence of these systems failing to regenerate, even on cars used mainly on motorways. It seems that on cars with a very high sixth gear engine revs are too low to generate sufficient exhaust temperature. Occasional harder driving in lower gears should be sufficient to burn off the soot in such cases.
If it is not successful, or the warning repeatedly comes on you should visit your mechanic, they can carry out a test to see how badly the filter is blocked & check:
- If the pressure sensors are working correctly.
- Remove the filter from your car & replace with a change over filter
- Get the filter cleaned with ultrasonic cleaning
- Replace the filter with a new DPF filter
DPF Filter types
PSA vehicles (Citroën, Peugeot and also some Ford, Volvo) have an active on board additive system with its own tank & pump system that automatically doses the correct amount of additive to the diesel fuel. This active type relies on a fuel additive to lower the ignition temperature of the soot particles and along with the engine management system, monitors the load of the filter with sensors & triggers a filter regeneration by altering engine timing & fuel flow settings.
The additive is stored in a separate tank and is mixed automatically with the fuel when you fill up. This system needs filling up of theadditive dosing tank with JLM Refill Fluid & equipment that involve system resetting & should be carried out by mechanics only, these systems now only require fluid refills at around 120,000klm.
- For this vehicle type with on board dosing system, JLM has developed the JLM Refill Fluid. Only to be used by professional mechanics, use only as replacement for corresponding listed numbers on the JLM Refill Fluid brochure.
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