Audi A5 2.0 TDI D.P.F fault cured

In the workshop today:









All new vehicles are fitted with D.P.F. (Diesel Particulate Filters) and we are seeing more and more with faults and blocked filters. At Branston Filling Station we specialise in D.P.F. problems and  are not phased by these problems in the slightest.

A lot of people and garages do not fully understand D.P.F. problems and there for they clean or fit a new D.P.F. and it then  blocks again and they don’t understand why. What you need to asses is the route corse and reason the D.P.F. has blocked in the first place. There are many factors that can contribute to a blocked D.P.F.  such as:-

Software problems – Some times the manufacturer will realise there is a problem with cars and bring out a software update, sometimes increasing the frequency in which the car regenerates to clean the D.P.F.

Temperature sensor faults- A D.P.F. has to get extremely hot to regenerate and there are temperature sensors before and sometimes after the D.P.F. to tell the Engine control unit the Temperature the D.P.F. is at. If these go faulty then regeneration will stop and the D.P.F. will block

Pressure Sensor faults – A D.P.F has a pressure sensor connected before and after it to measure the pressure difference. A blocked D.P.F. will have high back pressure from the pre sensor pipe which the pressure sensor measures to know when the D.P.F. is blocked.

Short journeys – It is always important to obtain information from the customer about the use of there vehicle. Due to the D.P.F. having to reach high temperatures to burn off the soot, if the vehicle only goes on short journeys (a few miles say) then switched off all the time the exhaust will not get hot enough thus causing the D.P.F. to block.

Ok on to the particular Vehicle in question here.

We recently saw one of many D.P.F. problems we get in for repair, an Audi A5 2.0 TDI. The customer brought the car in due to an engine light being on and the D.P.f. light being on.

First we carried out a diagnostic report using Autologic assist.

On checking the engine control module we have 3 codes:-

  • Bank 1 sensor 4 exhaust temperature sensor faulty
  • Exhaust pressure sensor faulty
  • Partial trap efficiency above threshold

Ok first of all we look at the temp sensor fault. This fault is basically saying the car has detected the temp sensor is not reading properly. On checking live data the temp sensors are all reading ok when running the engine up there all going up well over 100 degrees apart from sensor 4. this one is staying on zero.

Next we go to the exhaust to physically check the sensors. On inspection we notice the rear most sensor is missing from the exhaust. This is sensor 4.   Some engines have 2 banks i.e. 2 cylinder heads, such as v6 engines which would have bank 1 and bank 2.  The engine in question is a 4 cylinder in line engine and so just has 1 bank. Sensor 4 is the rear most sensor, hence bank 1 sensor 4.   On further inspection the sensor would sit behind the gearbox and you can see that the gearbox bolts have recently been removed. Probably to have a new clutch fitted. I contacted the owner and indeed it had just recently had a clutch fitted at another garage. Could they have forgot to fit the sensor back in when they were refitting the parts? it was looking very lightly that this was the main cause of the D.P.F. problem in the first place.

So we fitted a new sensor and rechecked the faults, this fault had now gone and the sensors were reading fine.

Next we look at the pressure sensor fault. We look at the D.P.F. soot content mass on live data and notice it is very high 50 grams. We next read the pressure from the sensor it doesn’t move and is stuck at 5kpa. We suspect the sensor to be faulty due to the back pressure from the blocked D.P.F. which has over pressurised the D.P.F. We remove the pressure pipes from the sensor and check the actual physical pressure with a mity vac when the car is started the pressure shoots up indicating the D.P.F. to be blocked. So we fit a new pressure sensor but temporarily leave the pressure pipe off so not to damage the new sensor.

Next we need to clean the Dpf and get the soot content down to a level the car will then regenerate and burn the rest of the soot off. We remove the front temp sensor and use our liquid molly D.P.F. cleaning gun and spray the D.P.f. cleaner into the D.P.F. and leave it to disolve the carbon. Then we inject a purge into the D.P.F. to flush it threw. Next we refit the temp sensor and start the car leaving it to idle and slowly clear the soot from the exhaust by burning it off as the car warms up.

Now we reconnect the pressure sensor pipe as the pressure is now at a safe level.


When the car is put to temperature using our Autologic diagnostic we force the car to go into a regeneration cycle. This burns all the soot off.

We road test the car and as the car is regenerating we look at the soot content on live data. We drive the car until the soot content reaches zero. This takes about 20 miles. We then check all sensors are reading correctly, and voila!!

The car is good as new again and ready to return to the customer. This saved them the cost of a new D.P.F.


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