What RPM were you driving it at on the motorway?
I took mine out for a motorway run once with the aim of making sure it was clear (the light wasnt on but i thought i'd play it safe and make sure it was clear anyway, last thing i wanted was the light comin in when stuck in a traffic jam!) but was only cruising at about 1500rpm and the light came on after about 10 minutes!
Sods law or what.
Anyway, my point is, it needs a constant 2,200 rpm to clear it.
(I've also tried giving it some serious stick to clear it when the light came on once, going for a full rev range assault on the a57 out towards snakes pass... ended up going into limp mode and an hour long wait for the AA man to come tow me back home. doh!)
The DPF cycle is a continuous cycle, the soot loading will gradually creep up regardless of how you drive and when the soot loading gets to 45% a regen will kick in. when the soot loading is low enough the regen will stop and the cycle will begin again of soot loading gradually creeping up.
In my experience of monitoring with Vag-Com on long journeys, Driving so as to clear the DPF when the ECU isn't in regen will do nothing to reduce your soot loading. you need to actually be in a regen in order to clear your DPF. I drove mine for 3 hrs on the motorway one time, I started off with 14% and ended up with 28%. This was doing 80 on the cruise just over 2kRPM
Another note is that when you have a DPF light on it means that a normal regen was interrupted 3 or 4 times and the light tells you to drive in a way that assists the regen process. When the light goes off the soot loading will not be 0% but just enough to make do. You should carry on with the regen driving after the light goes off (on the same journey) to get the soot level right down to 0%
This may be of interest to you if you haven't already read it.
There are 2 types of regeneration, passive and active
During long motorway journeys, passive regeneration will occur. This needs no intervention from the engine control unit. Due to the raised exhaust temperatures on a long journey
(temperatures between 350 and 500°C), the procedure occurs slowly and continuously across the catalytic-coated (with platinum) DPF. The catalytic-coated DPF is situated
close to the Engine, therefore the exhaust gas temperature is high enough (500°C) to ignite the soot particles.
Due to this soot is burned-off and is converted into a smaller amount of ash.
Active ‘regeneration’ is when the ECU intervenes when the soot loading in the DPF is calculated to be 45%. The procedure lasts for about 5 – 10 minutes. Specific measures are taken by
the ECU to raise the engine exhaust temperature to above 600°C, these include switching off the exhaust gas recirculation and increasing the fuel injection period to include a small
injection after the main injection. The soot particles are oxidised at this temperature.
The ECU will trigger a regeneration process, if for some reason this is aborted, ie. customer slows down, stops etc, the process will be resumed when
regeneration conditions are once again met, above 60km/h (38mph). This will continue for 15 minutes.
If after 2 attempts of 15 minutes, a successful regeneration has not been possible, the loading will increase. At 50% soot loading, the ECU will continue to
maintain maximum exhaust temperatures of 600°C to 650°C to cause a regeneration process. The system will try to run a regeneration process for 15
minutes. If unsuccessful, the system will repeat this process for a further 15 minutes, if still unsuccessful, the DPF light on the driver display panel will then be lit.