Where is the DPF system injector?

You mean doser injector? If so, should be behind turbo

 

Usually their are two. One is just behind the turbo. That one is used for active regeneration while driving. Then other one is by the DPF and is used for parked regeneration. That's how Detroits and I believe Cummins are set up

 

The seventh injector refers to the injector next to the DPF filter. The ones used for parked regeneration. Unless paccar is different

 

It's behind the turbo, ahead of the DPF.
Not rocket science.
You will need something to catch a lot of your coolant, because it is cooled.
May or may not need to update your ECM as well.

Look at RAWZE on UTUBE. He has step by step for Cummins doser.
Paccar same principle.

 

How many hours on the engine and how long since it was last it cleaned? They plug up with soot, we clean them every 4500 hours with the DPF cleaning. Same with the DEF doser in the pipe between the DPF and SCR system. Not hard to do, but you do have to drain the coolant. Use come carb cleaner and a brass wire brush. A clogged doser is the #1 cause for a not responding fault.

 

No, you cannot clear the fault without the software. If you fixed the issue, the lamp will clear eventually. It may clear after the 1st successful active regen, it might take 2 regens. I don't remember off the top of my head how many, but the fault will stay "pending" until certain conditions are met for it to change to inactive. Did you do a parked regen?