I have an on going issue that my mechanic and I could use some input on. 2015 Ranger, auto, 2.2 diesel.

A few months ago my DPF warning light began turning on, and then a few days later my check transmission ( automatic) warning light would go on, than a few days after that both of those warning lights would go off and my check engine light would come on. Since it was always in that order, we assumed the first caused the second.

We forced a regen twice and never received an actual code for the automatic transmission light.

We finally replaced the DPF but it did the same sequence after the replacement. We then thought that one of the sensors that we had to replace, as it would not come out of the old DPF, was the culprit and so we replace that. We thought we had succeeded unfortunately a day later it began again only the check transmission light came on prior to the DPF light coming on.... which suggests they are not related, at least in the causal relationship we thought. We still get no code from the transmission and the DPF codes say that the dpf is sooting up and it wants to regen although it cannot be as temperature before and after is the same and it doesn't have even 200 kilometers on it. My mechanic is pulling his hair out as am I. Has anybody encountered something similar?