Bad exhaust temp

Hydrocarbon doser maybe?

 

Probably not the fuel doser, that's not hot enough for it to even start dosing. Did you check for exhaust leaks? What is the coolant temp? If this is a CM871, check injector cam timing. Those engines had lots of cam timing issues preventing parked regens because they can't build enough heat. Most of the time, if the cam timing was set wrong, the air compressor is noisy when building air. I'm not sure why, but I've fixed a dozen or so for that same issue and once timed correctly, the compressor quiets down and it starts building enough heat to regen. If the compressor makes noise and gets quiet as soon as it unloads, retime the injector cam.