Audi A4 - Audi DPF SENSOR - jhs2hm
I have an Audi A4 2.0 tdi 58 plate (2008) standard uk spec. My engine management light came on and I've been told the code means I need a new G450 DPF Sensor. I'll have this fitted later in the week but what I would like to know is will the DPF just continue to get clogged up if I continue driving or will the normal burn off still occur if I am doing only motorway miles at high speed? I think this may be called "passive regen" where the burn off will occur by default if I get sufficient temperature build up. But I am unsure if a faulty sensor will also stop this auto burn off from occurring. I am assuming the active regen which the car would almost certainly use the sensor for will not currently be working if the sensor is faulty. The dpf light has not come on at any point. It is only the engine management light that is on.
Audi A4 - Audi DPF SENSOR - craig-pd130

I had a DPF sensor fail on my Volvo V60 about 20 miles into a 250-mile A-road / motorway drive (the emissions light came on, the car didn't go into limp mode). When Volvo Assist came to read the diagnostics the next day, I asked him to check the DPF soot level and it was under 5%.

If you're doing m/way driving at speed, the DPF will burn off the soot passively.

Audi A4 - Audi DPF SENSOR - Railroad.
Firstly what makes you suspect that the sensor itself is faulty? Secondly the engine is controlled by the ECU, and not by you the driver. The ECU will regenerate the DPF when driving conditions are met to do so. This is typically at a constant speed of 50mph or so with the engine at normal running temperature. There is nothing you can do to speed up the process. Belting ten bails up the road will achieve nothing. The ECU will stop the regeneration process if you do.

If it will not regenerate then a forced regeneration will need to be carried out. Find someone with VCDS to do it for you. I have that and I'm in Hampshire if it helps.
Audi A4 - Audi DPF SENSOR - craig-pd130

I think the OP is asking if the DPF will risk getting full of soot in the next couple of days, before he has the sensor replaced, as he has a few motorway journeys to do. I don't think he is planning to cane the engine in an effort to regenerate the DPF.

In m experience with the Volvo above, the soot level in the DPF will not build up during a long open-road drive, and there will probably be some passive regeneration.

Audi A4 - Audi DPF SENSOR - Railroad.

I think the OP is asking if the DPF will risk getting full of soot in the next couple of days, before he has the sensor replaced, as he has a few motorway journeys to do. I don't think he is planning to cane the engine in an effort to regenerate the DPF.

In m experience with the Volvo above, the soot level in the DPF will not build up during a long open-road drive, and there will probably be some passive regeneration.

My question was what makes him certain that the sensor is faulty? How can the ECU tell the difference between a sensor giving little or no output signal due to a sensor fault, and a sensor giving little or no output due to a blocked pipe? Either way the ECU detects no signal. This is why sensors are very often incorrectly blamed for faults that lie elsewhere.
Audi A4 - Audi DPF SENSOR - craig-pd130

My question was what makes him certain that the sensor is faulty? How can the ECU tell the difference between a sensor giving little or no output signal due to a sensor fault, and a sensor giving little or no output due to a blocked pipe? Either way the ECU detects no signal. This is why sensors are very often incorrectly blamed for faults that lie elsewhere.

True - hopefully whoever read the code had a look at the pipework too.

Mind you, if VAG engines have a diagnostic code for DPF sensors, at least they're a step ahead of Volvo. When the differential pressure sensor failed on my V60, the fault code was EGR related (EGR flow out of range), so the dealer replaced the EGR valve and pipework first, which obviously didn't fix the problem. Good job the car was still under warranty.

Audi A4 - Audi DPF SENSOR - jhs2hm
Thanks for the replies. I had the code read at an Audi specialist who informed me it needed a new sensor. Doing some online searches it does appear to be a common enough problem. It's booked in to be replaced in a couple of days so hopefully I don't get any issues during the 200 miles I still need to do which will all be motorway driving.

I had thought the ecu uses the sensor to determine whether a regen is required and would then initiate the active regen. Also I was under the impression that a higher temperature is reached when doing high speeds and in a gear where it's between 2-3k revs and during this the higher temperature would automatically burn off any residue without the need for the ecu to initiate any regen.

So the main point of my question was whether the advice of clearing up a partially blocked dpf by taking it high speeds on a motorway is just due to the temperature it achieves or if that in turn triggers the sensor (which in my case allegedly doesn't work) to get the car to do a regen.
Audi A4 - Audi DPF SENSOR - craig-pd130

DPFs do 'passively' regenerate at open-road speeds but don't need high revs to do it, the engine just needs to be under a reasonable load which means somewhere near the peak torque (i.e. usually around 1,750 - 2000rpm in the higher gears).

However I'm not sure this will fully clear the DPF in the same way an active regeneration will. Only the ECU will decide when an active regen happens - usually at a given % of soot loading in the DPF, or at a given mileage interval, whichever comes first.

Audi A4 - Audi DPF SENSOR - Railroad.
There are two pressure sensors, each with a pipe connected to either side of the DPF. The ECU is monitoring the two and comparing the readings. Similar readings indicated a clear DPF, while different readings mean it's blocked. If the small pipes become blocked or damaged then the ECU will may not be able to read anything at all and so in that case a sensor fault will flag up. This doesn't necessarily mean the sensor is faulty, it simply means the ECU isn't receiving anything from it. As a previous poster has said, I'm sure your garage has checked this though.
Audi A4 - Audi DPF SENSOR - Railroad.
Firstly what makes you suspect that the sensor itself is faulty? Secondly the engine is controlled by the ECU, and not by you the driver. The ECU will regenerate the DPF when driving conditions are met to do so. This is typically at a constant speed of 50mph or so with the engine at normal running temperature. There is nothing you can do to speed up the process. Belting ten bails up the road will achieve nothing. The ECU will stop the regeneration process if you do.

If it will not regenerate then a forced regeneration will need to be carried out. Find someone with VCDS to do it for you. I have that and I'm in Hampshire if it helps.
 

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