Found thisin another thread... explains my issue. "have a 3039R Cab tractor that has this same issue. It did a regen at 1500RPM's and only reduced the soot levels minimally. I tried to initiate a parked regen, but it also would not let me. I notified the dealer and he came out to see for himself what the tractor was doing as he had not heard of this before. He encountered the same thing I did, could not start a parked regen. He reached out to the Deere service rep for our area, who indicated that you can not run a parked regen for at least 50 hours from the previous passive or parked regen. The tractor can initiate a regen if necessary within that 50 hour wait, but you can not start one manually. Also, said that if need be, the tractor can be brought in under warranty and the dealer can perform a "service regen" to return soot levels to zero. Hope this helps. I have continued to use the tractor and have ignored the soot levels. I know the dealer will take care on any issue I have if one arises. Best advice would be to notify the dealer of your experience in case it becomes an issue"