Audi Q7 (V8 TDI) DPF measuring blocks

Fault codes You can clear with any diagnostic equipment and they will not reappear unless all conditions for setting that DTC exists. But if You have or had DPF related faults that switched warning light on, successful regeneration is required to get it off again. Mainly all VAG diesel cars with DPF are made that way. (And not only VAG).

Good evening gents (uk time!)

Had some developments today. Decided to replace the bad glow plug with a view to then driving up and down the motorway for a while to try and clean the dpfs.

However on the way to the parts place Got some new symptoms:

- Flashing coil light with limp mode (vastly restricted power)

- MIL light on with code P242F Diesel Particulate Filter (Bank 1) Restricted/Clogged stored in both engine modules #1 and #2

I decided to change the glow plug anyway and drive the car in a suitable fashion to try and achieve dpf cleaning. This was very difficult in limp mode. Next I tried clearing all fault codes with vcds whilst driving. This allowed me to drive with full power for around 20 seconds each time but then the clogged dpf code returned to both ecus and limp mode conditions occurred once more. I tried this several times but each time after approx. 20 seconds the fault code and limp mode returned

Im thinking now that next I need to clean the dpfs manually. So I will remove them and soak them in some industrial dpf cleaner, jetwash clean, etc.

In respect of the useful theory Uwe presented about possible hollowed out dpfs- I gave you some bad info there. I rechecked today whilst in the car and there is indeed a small amount of pressure drop (7mbar) across both dpfs at idle (as you correctly said there should be. Sorry Uwe)
I also looked at the dpf pressure drops whilst driving at 60mph and both dpfs were showing pressure drops of around 50mbar

The problem I foresee is that after cleaning them the car will still be in limp mode with a dpf caption until a regeneration happens, as Martin has suggested above (thanks for the good info there) I also suspect it will not regenerate whilst in limp mode.

As an experiment I tried clearing all fault codes with vcds with the engine static, Thinking that the dpf blocked caption and limp mode would not return until the engine was started and consequently the control modules started getting the clogged readings from the sensors. HOWEVER, this was not the case. The fault code and flashing coil light (limp mode) returned without starting the engine after 20 seconds or so.

So my question is gentlemen: How do I reset limp mode and the dpf warning once I have cleaned and re-fitted BOTH DPFs??????

Many thanks in advance for any help you can throw my way

Regards, Ben.

Based on the reported values, I'm not sure it's worthwhile to pull and clean those DPFs.

Short, full-power runs is not the way to burn stuff out of a DPF in any case. In fact, I think that might make things worse. Assuming you've got your glow-plug problem fixed, go for an hour-long drive on the emptiest motorway you can find at the highest speed that won't get you arrested.

We'll need to do more digging for a procedure for this engine.

-Uwe-

LoL.....
OP could also select a lower gear to raise RPM and respect the speed or safety , however, it indeed would not be as fun.

Morning Gentlemen.

Many thanks Jack and Uwe for your ongoing support with my issue. I take on board all of you advice.

I did indeed replace the bad glow plug fault (code now clear) and then i drove for over an hour at over 2000rpm.
I believe that the car will not accept that the dpfs have been cleaned to within acceptable limits without somehow resetting limp mode first.

I believe that I can fix this problem one way or the other. However the thing thats now holding me back is this limp mode that im stuck in. I believe its not possible to sort this out without a limp mode reset procedure.

Uwe, If you can do some digging for a VCDS limp mode reset procedure for my vehicle then that would be awesome. I will hold off pulling the dpfs untill i find out how to carry out this reset and then go for a long drive.

Regards, Ben.

Hello Gents...

I drove the q7 for over an hour at over 2000rpm again yesterday. The dpf warning has now gone. However the car is still stuck in limp mode.
I am fairly sure that I need to use VCDS to carry out a forced regeneration before it will clear limp mode.
Unfortunately It is not obvious how to do this as its non-uds format.

Please can you share any information on how to carry out this procedure.

Many thanks.

Ben.

benr8440667 said:

The dpf warning has now gone. However the car is still stuck in limp mode.

Click to expand...

I would suggest that before making any assumptions about what problem(s) remain (if any) you should clear all fault codes and do a new Auto-Scan to see what fault codes are current.

If the fault codes don't return then maybe, just maybe, clearing the fault codes will remove limp mode?

PetrolDave said:

I would suggest that before making any assumptions about what problem(s) remain (if any) you should clear all fault codes and do a new Auto-Scan to see what fault codes are current.

If the fault codes don't return then maybe, just maybe, clearing the fault codes will remove limp mode?

Click to expand...

Sure sounds like it's worth trying -- and in both ECUs.

-Uwe-

FIXED!

Finally managed to get the “dpf bank 1 blocked” fault code with limp mode Fixed. Just thought I’d post the solution in order for others to benefit.

Given that I was unable to work out how to use vcds to reset/clear the fault code+limp mode after chemical cleaning and that no solution could be found here I decided to bite the bullet and take the car to a VAG specialist

What they did was firstly try VCDS as this was “usually quick and easy” however the specialist found (as have I!) that VCDS and a 2007 Q7 4.2tdi engine control modules don’t seem to get on very well! And couldn’t get anywhere...

Next They got out an old VAS main dealer diagnostics computer. With this they were able to reset both DPF adaptions and reset both DPF pressure sensor adaptions. There was lots of holding the revs high with foot on throttle for 5 minutes at a time too, instructed by VAS (Possible manual cleaning) Fault code gone. Limp mode gone.

Since then I have monitored the pre-dpf temperatures and the DPF pressure drops whilst driving (using VCDS) and all is normal and healthy.

Thanks to anyone that posted on my thread.

Regards, Ben.