Hi. I have 2004 350z touring, 90k miles.
I ran into a common 350z problem - one of the fans stopped working (passenger side) and thought it was an easy fix - fan motor died, needs replacing. I bought a brand new aftermarket fan assembly and installed it - problem didn't go away. So I thought may be they send a bad one for me, called the store, they offered exchange, send another one - same thing. So I checked the fans they send me the first time (connected straight from the battery) and they both worked.
So I switched the connectors of the fans from one to another and the other fan started working (driver side).
I ran IPDM auto active test, where IPDM sends signals to the cooling fans and one fan worked on both Hi and Low speeds but the other one didn't work at all. I checked 2 fuses in the fuse block - they seemed fine to me.
In the manual it says that the problems could be:
- Harness/connector malfunction between IPDM E/R and cooling fan
motor
- IPDM E/R (integrated relay) malfunction

Any other things I should think of?
Should I just change the whole IPDM module?
Or is there any way to just change the relays there (i read somewhere here that you can't do it, it comes as a complete module).
Any other tests I can do to get more close to understanding the problem?
Any help is appreciated.
It is really hot in here and I don't want to toast my engine because of the freaking fan.

 

I'd follow the lines from the fan and work your way back, looking for a short somewhere in the harness. It sounds like the signal or power wire is toast. You can try jumping the power or signal wire with a new one to see if works as well.

 

Finally I found the solution. I wanted to check the wiring like zakmartin recommended but then I thought, it shouldn't be it since the car has never been in the accident. So I bought used IPDM from ebay for 60$ (has to be same car year) and replaced it.
Everything worked fine after that, both of the fans are spinning on both speeds.
So we should add another 350z cooling solution to the ones that we already have)
Besides the air in the system, thermostat, blown fan motors, cracked radiator or not enough coolant there is IPDM that has fan relays that might go bad as well.

 

The IPDM and BCM themselves do short, relays shouldn't go bad like that but you know "if it's not one thing, it's the other"

Good stuff fixing the Z

Also renamed your thread to help others find/search for your thread via google or the search functions

Thanks again for updating with a fix action