I seek knowledge from the wise ones

[X5Sport]

The regen cycle should happen every 300 miles or so. It will only do it if as said, the engine is fully up to temperature. Typically the recommendation is to take it for a drive where the speed does not fall below 40mph for at least 20 minutes - a 60mph run on a dual-carriageway/motorway is a great place.

On my X6, the clue is that if you stop mid-cycle all the engine fans will be running flat out to stop the red hot exhaust setting the car alight, and will run for up to ten minutes. Sounds like there’s an aircraft under the bonnet. If you’ve heard that then you know it’s running fine.

[sapphireblack]

I confess i have never experienced what you suggest. I was aware of the 40mph+ run and have done that specifically in the past, though have never been aware of anything happening. If fact i can do that tomorrow with some motorway driving.

[X5Sport]

If it’s completed by the time you get out then you’ll never experience it. I’ve only heard it about 6 times in 15 years.

[Leslie]

Cars should have a "doing a regen don't stop now " light

[sapphireblack]

Cars should have a "doing a regen don't stop now " light

That would make sense

[IanP]

If it was not reggening it would be blocked solid within a few 1000 miles..Its hard to spot a regen sometimes it holds a higher gear but its not obvious though if you get out mid regeneration you can feel the heat from the back of the car and slight burning smell at times I find.
The dpf could be as simple as thermostats keeping the engine too cold but its a gamble , I wonder what they were going to do for 1100 quid ? smash the centre out of the dpf and map it out like many of them do now when they see how hard it is to change .
I was following a 40d recently and the black smoke every time they hit the gas was silly , clearly dpf long gone.

Surprisingly a car without a dpf, or one which has been modified will not necessarily smoke. (Or fail the mot....)
A poor map or other mechanical problems will smoke however.
Some remaps are available that specifically give heavy smoke under acceleration, apparently it's a "thing" in some parts of the car world

[Leslie]

The new mot was rumored to properly test if a Dpf actually works by measuring particulates rather that just see its there even if nothing inside and despite all our mot centres here in Norn Iron being government owned and run we don't even test diesel emissions and never have in many years if ever .
Ian The smokey remaps are called "reek" maps over here lol

[Alan Gunn]

When i have requested a re-gen i can't notice it so when i do i run Bimerlink on my phone and watch the exhaust temp.
That is the only way i can tell.
I was surprised when looking at the DPF levels in my Merc (sorry for swearing) only last week as i had done many short trips 7 or 8 miles since last November.
On looking in the scanner the car had recently done a re-gen but i hadn't done a longer run strange.

[X5Sport]

I think the ‘longer run’ is the suggested way of encouraging (if that’s the right word) the system to do a regen. As long as the car gets warm enough for long enough it’ll work. At least that’s my theory.

[sapphireblack]

I undertook my two hours each way trip yesterday, principally the M25 and M23 to start. That was well over twenty minutes and 40 mph. I didn't feel or hear a thing, despite being very aware of what should be happening, which is kind of annoying in a way. It would be nice to know the process was done.

[X5Sport]

Without live diagnostics looking at the DPF data, I don’t believe there is any simple way. Some folks report a slight reduction in fuel economy whilst the cycle is running. I’ve never noticed it apart those rare occasions when I’ve switched off mid-cycle. The general view is it happens at least once per tank of fuel and you may get a small puff of white smoke at the end. Blink and you miss it! If your DPF light isn’t coming on then all is probably absolutely fine with the system.

[Leslie]

If it didn't need a regen nothing will happen anyway during that long run ,as said no lights you are good to go
, I always made a point of once a week using manual mode to get the revs higher to over 2k continously for 5 miles after a 5 mile warmup in a 20 mile run . That gives it a good opportunity to regen after a lot of short runs if needed.