Thanks for the diagram, if you can bear with me, I'm a little out of my element with complex electronics systems like this!
So if I understand this correctly, if I unplug the post catalytic NOS sensor and replace the fuse, start it, there's my problem. If it still blows the fuse, I might be in trouble.
Can you guys let me know, if I'm reading this correctly... The digital diesel electronics control unit is powered by both the number 4 circuit AND the number 1 circuit (20 amp)??
If the electronics control unit is bad, would it not blow both fuses?
I hate to say "hopefully" the NOS sensor is bad or the metering valve is bad. The sound of the "digital diesel control unit" scares the hell out of me!