Volvo DPF / SCR problems

yeah low voltage code so i checked and only red less than 1 volt so dealer changed engine ecu $1,600 fixed that problem. so next step is to pull valve cover and go hunting for bad injector that was possibly damaged by cracked valve that the first shop reinstalled without testing or i would of replaced.

 

I have a 2016 volvo vnl 670 that says dpf fault what does that actually mean? Ive been having to regen more. Iwas going to replace the def fuel filter. But i don't know if that will fix the problem please help my name is bobby

 

Would Mack codes apply here? MP8 P01162A 202D00 code. I cant read running DEF pressure but the pressure buildup test does not seem to hit the target pressure.