Before I start throwing money at my radiator fan assembly, which stopped working today, I am ordering a relay first. But my question is whether or not one side stops working first or is it an all or nothing situation. Its not a fuse question so its either a relay problem or I need a new fan assembly. Being an 8 month G35 owner I have no frame of reference but other cars I have owned the fans were coordinated but failed independent of each other.

 

If you have the straight dual electric fans. One side can fail while the error will still work. Three relays control the speed of the fan. My original OEM fan worked, however, the motors were weak and incapable of running fast enough to cool the engine. My replacement lasted barely a year and the A/C side first stopped working. The other side than failed and both motors burnt out and seized up and when I took them out I couldn't spin them by hand.

 

I'm wondering if ordering one relay will solve anything since you made no mention of a "main" relay, just the three. I have never seem anything like this in all of my years working on different makes. Usually the part is bad, a fuse, relay or fusible link but never the whole part with no individual fan relays, just fuses.

 

Yep, depending on how many of the relays the ECU turns will determine how fast the fans spin.

1 - Off, 2 - Off, 3 - Off = Fans Off
1 - On, 2 - Off, 3 - Off = Low Speed
1 - On, 2 - On, 3 - On = High Speed

There are four pins on the motors as well, so if you provide power to one of them and ground it runs at low. If you provide power to two of them and ground to the other two it will run at high speed.

If you tested all the relays and your A/C works as expected; I would assume it's your fan motors. The original ones had a TSB I think for the motors wearing out.

You can buy individual motors instead of the whole assembly.