I have an 03 Infiniti g35 sedan that’s manual and nothing wanted to work, like the windows didn’t roll up and down, didn’t want to lock or unlock, interior lights didn’t work, the gauge cluster didn’t even want to fully light up, and it just cranked. The previous owner changed out the harness and fuse box that’s behind the battery and runs into the cabin. Checked and it was the right fuse box but idk about the harness. I got all the electronics to work now. Messed with the interior fuse box and the module that’s connected to it and everything started to work.

Now all that’s left is to get it to start, which is the problem. The car still doesn’t start. I put the key in and the security light flashes but when I go to start it, it stays solid. I thought maybe it’s NATS so I had a key programmer come to check it out and he said that the chip in the key is fine but his computer didn’t even want to connect to the car. Strange, so I grabbed my scanner, trying to scan the car, and it powered on when I plugged it into the OBD2 port but when I went to go scan anything it said it had no communication. I just got done looking through all the fuses and all of them are fine except the bunch that power the headlamps and front washer switch (fuses 83,84,85,86,87) I was wondering if anyone’s got any idea what could cause that? I’m starting to think that the ecu is bad but how would I test that. Any input is appreciated cause I’m kind of stumped

First check your CAN and battery voltages at the DLC connector. There has to be 12V power on pin 16, many scanners won't connect without that even if there's ignition power on another pin. Your CAN voltages on 6 and 14 should be around 2.5V with the ignition on but should not be equal, CANL on 14 should read a bit lower than CANH on 6. Both voltages will be lower with the ignition off, but they should still be unequal and L should be lower than H. If you get abnormal readings then something is probably crossed or shorted with a CAN wire. If you get normal readings it means something on the bus is trashing it. It doesn't apply to your ride, but Frontier TCM's inside the tranny are infamous for going into "locked loop" transmission when they die, blowing up the bus with constant messages that crowd out all the other devices. Anything else on the bus can fail similarly, it just isn't as common. To identify that, try scanning with the key off. If you see only the BCM and IPDM, then the bus is okay but something ignition-powered is killing it. If that's the case, the only way to identify the offender is by pulling everything on the bus one by one and watching for everything else to wake up.