All new European diesel cars are required to be fitted with a Diesel Particulate Filter (DPF) in the exhaust system. This filter removes the soot particles from the exhaust gas which are collected, and build up on the filter medium. To prevent the filter from getting clogged, from time to time, it is necessary for this soot to be removed. It is burnt off by elevating the temperature of the filter to about 600 C for a period of about 20 minutes.
In Hyundai diesels, the method used to elevate the filter temperature, is to inject extra fuel into the engine towards the bottom of the firing stroke in each cylinder so that it burns as it passes through the DPF. This extra fuel does not increase engine power and is solely used for heating the filter. As a result, whilst the filter is being regenerated, the fuel consumption of the car will increase and cars fitted with an instant economy indicator will show a significant drop in economy.
Most of the soot collected in the DPF happens when you drive the car from cold until the engine reaches its normal operating temperature. During this period the combustion and exhaust gas temperatures will be lower than normal and more soot particles will be produced. Once the car reaches normal temperature less soot is produced. On very fast runs using high engine power continuously, the DPF may reach a sufficient temperature to burn off some of the soot. This may delay the need for the ECU to initiate an active DPF regeneration.
There are sensors built into the system which can estimate how much soot is building up in the DPF – one method being to measure the pressure drop across it. Once the soot loading reaches a set point, (whilst the engine is at its normal running temperature) the ECU will initiate an active regeneration. This usually takes about 20 minutes of driving at more than 40 mph. The time may be less if the car is travelling at higher speeds.
Unfortunately, there is no indication light in the instrument display to tell you that the DPF is being regenerated. The most visible signs are a sudden drop in the instant economy display, and for cars fitted with stop and go, it will be deactivated and the ISG button will illuminate. You may also notice the engine note sounding slightly rough. If a DPF regeneration has just occurred when you park the car, you may be aware of an unusually “hot” smell coming from under the car.
There are three schools of thought about how often the DPF is regenerated.
• Some believe it is at set intervals – like 250 or 300 miles.
• Others that the ECU waits until the DPF soot level reaches a set point
• Some believe it is a combination of the two – whichever comes first.
If you are aware that a regeneration cycle is currently taking place as you reach your destination – it is best to do a detour and drive at a minimum of 40 mph until it finishes before switching the engine off. There may be occasions when an active regeneration is taking place and you have either not noticed the DPF was regenerating, or you have no choice but to stop before the process has completed. If this happens, the ECU will log it as an incomplete cycle and will initiate a second regeneration during the following journeys when the DPF soot loading reaches a second set point.
If this cycle completes then the filter is emptied and whole process is reset to zero.
If however this 2nd attempt is not completed for any reason, like the journey being too short or you spend a long time in stop-start heavy traffic with the engine just ticking over. You will have a 3rd and final chance to let it do it's job.
The 3rd attempt will take place during a following journey when the DPF soot loading reaches a maximum allowable level. Again, if you allow it to complete, then the entire process is reset - but if you do not allow this 3rd active regeneration attempt to complete, the engine management lamp will light up and flash.
This is your last chance to let it do its job without getting the garage involved!
If the engine management light comes on and flashes continuously, take the car for a fast journey at approx. 60 mph with the engine spinning at around 2000 rpm, until the warning light stops flashing. This will give the ECU the opportunity to initiate a third regeneration, clear the DPF and reset the DPF cycle to zero.
If you ignore the warning light at this point, the DPF will become overloaded to a point where hard driving will not be able to clear it. At this point your only recourse is to take the car to a garage to perform what's called a 'Forced Regeneration'. This is unlikely to be free of charge!
WARNING
If you continue to drive the car with the warning light on – the soot will build up to a point where a forced regeneration by a garage is not possible and a new filter will be required. This is likely to cost around £1,500 and will not be covered by the warranty.
