On 22/08/2021 at 21:41, stever750 said:

 Once it's started, just let the car idle, it will complete the cycle, and faster than if you're driving it.

 

Are you sure about that?

 

It is contrary to the handbook advice where it says to drive above 65kph? and above 1800rpm? - both those figures are guesses from memory. And also contrary to the VAG documentation that I downloaded but dont have with me here in the UK to quote the details and the source.

 

Because of that if I arrive home and hear the radiator fans running I go for a drive on the rocade (by pass) until the idle revs drop again to 800rpm.

 

I would dearly love to just leave it ticking over if it would really work and really work faster than me driving it, however the only time I have had the DPF warning light was when I was doing the accident repairs & the vehicle was being started & stopped, moved a few feet each time etc, I heard the fans once and left it idling for another 30 minutes, the next time I started it I had the DPF light and had to take it for a drive except it was not yet roadworthy.

Absolutely sure, unless the app was misleading. First time I noticed it was driving around town, when I stopped the rate at which it was reducing the soot level increased when I was stationary. In fact, if I booted it, the rate occasionally started to increase! Makes sense, as under acceleration you're generating soot, the ecu assumes this (remember, it's not directly measuring this). When idling under no load, there is enough 2nd injector fuel in the regen sequence to maintain the required EGTs. I observed this multiple times, and yes it surprised me at first, but then I thought it through and made sense. Tbh, if I had another diesel I would use the app  continuously, that way you won't inadvertently switch the engine off midway through a regen, which is not good if its close to 100% soot level. 

To give an idea of how imprecise the system is though, I had occasionally had to do just that, turn off midway. By the time the engine had properly warmed up after the restart hours later, the soot level was over 100%, and still worked fine. 

Of course, the only way I could verify the function of the app was to check there was a regen taking place when the app was indicating it was, and every time I could check that (impossible at speed on the motorway) it was correct. Its a useful tool to monitor regen activity, I'm not convinced it's much use on predicting lifetime, though of course its simply relaying the info from the ecu, so use it accordingly; the point us that the ecu view of the DPF is possibly subject to significant error.