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My understanding, could be wrong, is that the 5 Volt reference from the ECU is a shared circuit in that all sensors have a 5V reference / signal like the Air Conditioning Pressure Sensor in your diagram above, coming from the same Pin Out on the ECU
If that is the case could a short in one drop the voltage in them all?
Gantocks, you are correct, if there is a problem with the wiring feeding all the devices that use that 5V reference voltage, then it would throw a lot of things off. A grounded component could pull the whole circuit down. If there is a break in the wiring, that would stop the voltage. This is where the easiest way to solve this is to unplug all devices on the 5V circuit and see if you are getting 5V at all points. This will tell you if you have any breaks in the wiring and/or if the ECU is outputting the 5V signal. From there, you can plug in the sensors one at a time, verifying that you still have 5V. If the 5V goes away, the last thing plugged in is bad and needs to be replaced. Not the quickest process, but in this case, because you have so many potentials, you need to reach a point that you know what is good and then slowly add the questionable components back in to determine what is wrong. Just because you find one thing wrong, keep on the path of replacing one thing and checking. You could potentially have 2 issues.
That 5V reference voltage gets around to several sensors. I'm not certain they are all the same 5V supply and not 2 or more isolated 5V supplies coming out of the ECU but thermo knows more than I so I would trust his recommendation to check all the 5V sensors. Here are the pin outs from the manual that I find that are 5V supply: