Hey all,
I've been having an issue with my 2004 350z. Basically the stock fans won't turn on, whether it's driving, A/C is on, or in the built in self test mode. I've verified that both fans work by connecting a power wire straight from the battery to the fans. Swapped IPDM and relays, swapped fuses, and replaced the rear engine coolant temp sensor. I'm about to give in and take it to someone who can properly diagnose, but wanted to see if anyone on here had any last ideas that I could try.

Thank you!

 

If you have a multimeter I would break it down into sections. I now you said you've checked the relays, but you can even have new parts fail which leads down a terrible rabbit hole. It's best to check with the multimeter to see if you are getting power to the relays.
I actually had my relay go bad, I believe it was number 3 in this diagram:



It is a strange part to fail, but it does fail. Same thing as you stated, would not come on during the on board diagnostic, but would turn on when power was directly applied.