RW,
I appreciate the offer and I will send you my email.
I agree that ultimately all power comes through the fuse box, that’s where the alternators, start power and emergency backup power all terminate. So in that way the fuse box is the power distribution center for everything to do with the engine. And yes, the fuse box feeds power to the ECU over two separate circuits, one to each lane. And if the fusebox fails completely, so does the ECU. No argument here.
But saying that the sensors run through the fusebox is misleading from a troubleshooting point of view. The sensors are wired directly to the ECU, and the 5 volt power supplies (for the sensors that require 5 volts) are within the ECU, not the fusebox. To the best of my understanding, there are no 5 volt circuits available at the fuse box. So if you have a 5 volt sensor that is not getting 5 volts (reference voltage), and the lanes are both powered and active, you would look to the ECU for the problem, not the fusebox. In other words, the upstream power source is the fuse box, but the power to the sensors is regulated and distributed by the ECU, and the return signal from each sensor returns directly to the ECU. If I am wrong about this I’m willing to learn, but this is how it looks to me.
