How to clean the DPF yourself
If you want to try and regenerate the DPF yourself first check the handbook for the specific instructions from the manufacturer. Believe it or not, not all manufacturers will have information relating to the DPF in their handbooks!
- Make sure you have the all important quarter of a tank of fuel
- The only light on should be the DPF light, engine management light and coil light are on this process will not work.
- The car needs to be brought up to running temperature before the process will start.
- Select a road where you can drive without stopping for 15 minutes or 15 miles
- Use an appropriate gear to drive the car at 2000 rpm and above 45 mph
- Once the process has ended successfully the light will go out.
This is not a definitive answer to all things DPF but I hope a useful overview on how they work, what can affect their function/process and how you can prolong their life span. It’s worth a read as it is rare that the DPF problem started with the DPF, more often than not the DPF is a symptom relating to another problem.
The DPF seems to me to be a bit of a Band-Aid applied to the diesel emission problem. Car manufacturers when creating a vehicle seem to be working from the tail pipe backwards as it is all about the tail pipe emissions. So the DPF’s function is to store the soot until it’s full, then during the correct driving cycle burn off the soot which then leaves via the tail pipe.
The criteria required for a regeneration means it is unlikely to ever regenerate in town meaning the inner city air quality is improved. Once the car is on the open road out of town the regeneration is then most likely to occur, so it won’t be long until we have asthmatic cows!
How a DPF works: So the DPF catches the soot from the engine and holds it until a certain amount of soot has accumulated, the engine control unit (ECU) will then wait until a type of driving cycle is met for it to trigger the regeneration process(Don’t forget also the requirement of a quarter of a tank of fuel).
Typically the driving cycle will be steady driving above 45 mph, accelerating, braking and stopping will cause it to abandon the regeneration process. So as you can imagine to keep a car running at a steady speed uninterrupted in the normal daily usage of the vehicle can be a challenge within itself.
During the regeneration process additional fuel is delivered into the engine to generate heat within the DPF, soot typically burns at 550 degrees celsius and above so this temperature needs to be maintained throughout the process. This causes the soot to burn off and each regeneration will leave a very small amount ash behind which remains trapped in the DPF.
After many regenerations the (ECU)will estimate the amount of ash that has accumulated within the DPF and flag a code relating to ‘Ash Accumulation’. This has been to now regarded as end of the DPF life.
‘Recent Examples of misdiagnosis’
We have come across a real mixed bag of faults which have all come to us under the banner of a ‘DPF fault’ below are a few recent examples.
A BMW X3 diagnosed by a main dealer as needing the cylinder head de-coking and DPF replacement, turned out to be a turbo fault and the DPF was fine. After paying £500 for just a diagnosis, and being given an estimation of £4000 he was pleased to have the car back on the road for less than half the main dealers estimated cost!
A Skoda Fabia kept being force regenerated by main dealer who overlooked low fuel pressure code, now fuel pressure problem resolved by changing the fuel filter, the car regenerates all by itself.
A Toyota Avensis before coming to us had already had a turbo changed and 2 x DPF’s fitted. Turned out to be carbon blocking one of the differential pipes causing a misreading pressure sensor. The misdiagnosis had cost the customer over £3000 before he came to us! Facebook link
A Toyota Avensis that had been diagnosed as needing a new DPF, when we attempted to clean the real problem came to light of a fault EGR valve. With a temporary fix to blank the EGR we successfully cleaned the DPF and replaced the EGR. Facebook Link
The Law has changed!
The government has introduced a change to the MOT as from 16th February 2014. If a diesel particulate filter (DPF) has been removed from a car that had one fitted as standard it will fail the MOT. This is a visual check only for the presence of the DPF and catalytic converter.
Notice issued to MOT stations
On 16th February 2014 Section 7.1 of the inspection manual will be amended to include a check for the presence of catalysts and particulate filters on diesel powered vehicles. Any vehicle where a catalytic converter or particulate filter is missing where one was fitted as standard will fail the test.
If you are planning to export or use the vehicle for ‘off road use only’ in other words do not require to have the vehicle MOT tested then you can still consider having the DPF removed. We would recommend though you carry out your own research on this.
Draft changes to the MOT for May 2018 are now available online to read, with reference to DPF’s there is a proposed inspection to see if there are any welding marks on the DPF case to suggest it has been tampered with. If spotted by the MOT examiner an explanation and supporting documentation will need to be provided for an MOT pass.
“Diesel particulate filters (DPF) should be checked for evidence that the DPF has been removed or otherwise tampered with. Where a DPF canister has clearly been cut open and re-welded, it should be rejected unless evidence can be provided that the canister was cut open for legitimate reasons, such as filter cleaning.”
You can read the whole draft here:-