The key reading you need is differential pressure - can you please report back (pref in millibars or hpa) what the reading is at idle and at 3000 revs ?
The active regen cycle on these Fiats is not complicated. The 68% is meaningless - it's just a figure the ECU works out from your driving style, time lapsed, miles driven, nothing more scientific than that. It has nothing to do with actual soot levels in the DPF, which is why so much confusion occurs.
Generally speaking, they will do a regen once the calculation is at 80% assuming certain conditions are met (coolant temp over 70, driving for at least 2 minutes, try to maintain 62mph, no engine management light).
Alternatively, once the percentage is over 100, the speed is irrelevant - as long as the other conditions are all met, it'll start regenerating (increasing DPF temp to 650 degrees), even at 20 mph. Just drive normally (even stop start is fine) and it should finish the regen within 10-15 mins.
Try to avoid forced regens if at all possible - if you try to do one of these when the DPF is blocked, you can crack it. The tail pipe test is a good gauge for this - wipe your index finger around the inside of the tailpipe. If it comes out covered in soot, your DPF is damaged. It should not blow any black smoke (soot) out at all.
Unlike other manufacturers, the DPF is poorly implemented in the engine management system. There are only about 4 codes - the two key ones are P1206-22 (level 1 blocking reached) and P2002-22 (level 2 blocking reached). This will appear when the differential pressure is high, but the computed percentage clogging is low. It's then a case of having to try to work out why the differential pressure is high - usually soot getting in from somewhere that the engine hasn't taken into account - can be leaking injectors, dodgy EGRs, blocked oil feeds, blocked coolers, dodgy sensor, blocked sensor pipes, you name it).
Putting DPF additive in the fuel tank is one option, but not guaranteed. You're far better to try some of the DPF foam cleaner (Mannol do one), as it works on dissolving the soot in the DPF, then combusting it through normal engine temperature
.
Hope this helps - I've become a bit of a DPF bore since buying my most recent Doblo. If you have any DPF related questions shout up.
