No, some fuses only light up when the key is on start, but most of those fuses the key does not have to be on at all.
The ECU or PCM as it is called nowadays has a few power feeds. They are pin 66 a red/black wire, that comes from dedicated fuse #4 in the engine compartment relay box. Then there is pins 41 and 47, 2 red wires which are spliced together and come from that MFI relay and before that dedicated fuse #13.
They all should have 12 volts, with the key on run. Although the fuses are hot all the time with 12 volts.
Some of them you are checking at the PCM might be the ones that are only supposed to have 5 volts, like to power sensors. That may be why they appear low, but that is normal.
Tuesday, December 26th, 2017 AT 6:41 AM