What's the difference between passive and active regen?
Short version: Regeneration is the process of chemically changing particulate matter (soot ... which has been trapped by the DPF) into more-acceptable exhaust products.
The process requires a certain heat level.
"Passive Regeneration" takes place as a matter of course, unrecognized by the driver, whenever driving conditions (speed/load) are such that sufficient high temperatures are generated in the system.
"Active Regeneration" occurs when passive regeneration is not accomplishing sufficient soot removal, thus the filter could become clogged as a result of soot accumulation, so sensors direct the injectors to place additional fuel in the exhaust system, to raise the temperature of the gasses to a degree where the process can proceed. This additional fuel raises the EGT, so that the process can be observed by the driver who is monitoring gauges, and notices a sudden, otherwise-unexplained EGT increase.
Ideally the "Active Regeneration" will be initiated only as actually needed, so that excessive fuel consumption will not result.
It seems that getting all the bugs out of the system is taking a bit of tweaking,... thus the series of TSB's and "flashes".
You might want to search-for and read the thread titled "Understanding regeneration".
