Apologies for the essay, but I think this info might help some people.
I've had some success in using the OBD-II interface to detect when my '57 reg Focus 1.6 TDCi is doing a DPF regen cycle. Thanks to a previous post, I have discovered that the EGT reading comes out on mode 22, PID 0992. I'm using the Android Torque app with one of those £12 Chinese BlueTooth ELM interfaces. I have it configured to send 220992 and the result is 2 bytes of actual sensor data, which appears to need the standard ((A*256)+B)-40 to turn that into a degrees C reading. My guess is that this really is degrees C. It won't read lower then 100C and quickly starts rising from there about 30s after a cold start. Trundling around town gets me about 200-250C indicated and motorway cruising at 60-70MPH gets 300-350, depending on load.
One night on the way home, I put my foot down going up a hill on a dual carriageway and it took off: 400... 500... 600... and topped out at 611C on my rudimentary gauge. Unfortunately, I was only 3 minutes from home and it's downhill all the way. Coming into town I could see that the ECU was trying to keep the EGT up above 500C. I went round the roundabout and back up the dual carriageway and let it finish its business. This was noted when about 10 minutes later, the EGT started to plummet and quickly got back to around 200 as I arrived home. On tickover, it's 150-190C.
In past days, I've seen it start a regen cycle approximately every 150-200 miles. Because it has no real intelligence, it always seems to do it JUST before I get home, or get into heavy traffic, or get off a fast road. Other interesting phenomena: A regen cycle is preceded by the intake air temp rocketing up from say 5C to 50C in just a few seconds. I'd wager that it was closing the intercooler bypass. If I didn't have the OBD gauges, I wouldn't know it was happening. No discernible difference in performance, instant MPGs or coolant temp.
Thanks to other posters, I am also able to get what appears to be the DPF differential pressure reading out on 2209E2, but this info is useless to the layman. Treating the 2 bytes output as separate hex digits seems to work: ((A*256)+B) gives a reading that tracks RPMs and engine load. As might be expected, there's a HUGE disparity between tickover and motorway cruising.
I tried to normalize the reading by dividing by RPM but that doesn't work because you could be at 2000 RPM with 15psi of turbo boost, or you could be at 2000 RPM with your foot off the pedal, decelerating down a hill. Also tried dividing by MAF reading, but that's no good either.
I have come to the conclusion that the differential pressure reading is utterly useless on its own for determining % DPF loading (blockage factor). I am sure that the ECU in the car must populate some data table while you're driving and can thereby, over a period of time see a gradual increase in differential pressure against a calibrated set of characteristics programmed by the manufacturer.
As Maertl says, what we really need is to find the OBD-II PID that tells us what the ECU's calculated % reading is. I can understand why manufacturers don't display this information to the driver - I've nearly gone off the road several times, obsessing and tinkering with my EGT gauge. On a commercial airliner which flies itself for 90% of the journey, it's quite OK to have 100+ gauges telling you everything from the EGT on 4 engines to the toilet flush water level. Not so in a road-going car.
In conclusion, I need to do what this guy did: http://www.phones-direct.ro/public/f.../index-uk.html
and build my own microcontroller-based gauge that gives a simple bar graph EGT reading. Coupled with an audible beep whenever a regen cycle starts (i.e. EGT goes over 500C) and job's a good-un. I can use the OBD EGT readings to calibrate the analogue measurement from the sensor, because it's sure to be non-linear. The big advantage of having a separate, analogue measurement of EGT is that it doesn't tie up the Bluetooth on your phone, having an OBD app running all the time.