I have searched through this forum, but found only some dead ended links to nothing about the radiator cooling fan wiring. Neither cooling fan comes on, I replaced both of them, ALL 4 relays under that long black cover on the engine side of the firewall, the switch that goes under the thermostat, the thermostat itself & the radiator that was kinda leaking anyway. Whole new cooling system? Yes. Needle still going over 3/4 of the way over on the temp scale? Yes. I freak out in slow traffic & crank up the heat to lower it down some, that does kinda work, but it is already hot & humid in the midwest already. If I am on the highway, no problem, stays under 200. It wont come on with the AC either, and that also does not work. Is there something I am missing? I was thinking about making a switched connection to the larger fan that I can control manually, but I would like the keep from that if possible. I sure could use a useful diagram of all the wiring on the fan circuits. Mine is a 1996 ssei Bon with about 230k on the odometer. Please help! I do not race it, I just like to drive it. It is all I have to drive.

Have you checked all fuses in the I/P fuse block and the passenger side fuse block?

Try this, disconnect the coolant temp sensor, then start it. The fans should come on and stay on. Not sure if your Check engine light will come on. It does on my 95, but not on my 97. Let us know what happens.

You said you are a 96? I don't have a wiring diagram for your year (or even 97 for that matter...hey Dan!), first things first though, the fans should come on low speed at 216F and high speed at 228F.

The pcm controls the fans via a ground trigger. If you can verify that the system is up over 216F (a scan gauge would be the best way) then check for ground at the low speed relay contact. If you don't have a ground present check the wire from the relay to the pcm (96 and 97 are wired the same, so the pin locations and colors Dan could provide should be on the money for you). I would also check the ignition power side of the relay actuation, this is probably as easy as missing ignition or ground to actuate the relay.

In the meantime, here is a quick bit of info on how to build a fan override that should also help you with the relay wiring and colors that you'll be looking for. If you did this, it will trigger an SES light, but it will also turn the fans on at your command.
https://www.gmforum.com/showthread.p...t=fan+override

Thanks for all the useful replies. I did check all fuses, they are all good. The fans both came on when I disconnected the temp switch plug just under the thermostat housing. I am going to try this fix tomorrow, but I am still curious about what could be making the fans not come on in the first place. Any ideas?

With the coolant sensor unplugged the pcm should be requesting fans as a failsafe. With the AC on the pcm should automatically request the fans. When temp reaches X amount it should kick on fans.... hmmmmmmmmm

When you kick on the AC, does the AC work? I'm reaching on this one, thinking that maybe there'* something up with the AC system and the pcm isn't requesting the fans because it see'* a fault in the AC system. Doesn't yet explain the request on high temp etc, but I'm working up to it.

No fans with the a/c on, so your theory holds lots of water for me. I bought this car last fall, and the a/c worked great, now it just blows hot air. I also noticed an odd thing - I thought the firewall on the engine side of my car was orange, but it turns out that the plastic for the a/c system that goes around the blower motor, and a ways away from it all around, is rotted & falling off. Mostly insulation is showing now, but all the wiring looks solid.

Ok guys, here is the new wrinkle in my fan cooling down situation. I found the 2 relays to the right of the maxifuse center. I found the little blue wire that when grounded, kicked both fans on. That did not work until I plugged the fan switch under the thermostat back in. Then, I went to the relay right next to it, still on the right side of the fuse center, there was a large light blue wire. I tried to ground it, then it sparked & I took it off within 2 seconds. Now the fans wont come on for anything & the car is hard to start unless I rev the gas some, then she runs fine. After all this, I un-hooked the battery for 30 minutes to let the control module reset (hopefully). I also went through & checked ALL fuses, both under the hood & under the steering column. They are all good. I also swapped out the 2 relays on the right with the 2 relays on the left since they all have the same numbers printed on them. Still cannot get my fans on, not even with the thermo switch un-done or the little dark blue wire grounded. Can someone tell me if I fried something? Pretty please with a beer on tap!

You mighta. Double check the fuses under the hood in the maxifuse center. Each relay gets it'* power from a fuse right there. Which means that you should have blown one or come close to blowing it.

Anyone with a 96/97 FSM have a moment to look up the relays and find out which one has light blue power wire feeding it?

Even stranger, the engine runs fine again, but the tranny wont fully engage now, seems like it is slipping on low fluid, which is not the case. This started after I accidentaly grounded the light blue wire in the low speed fan relay. All fuses still check out fine. Can someone please tell me what i broke please?

Without being there to diagnose it in person, it'* quite hard to tell you what you broke. Please keep feeding us info and we'll do our best.

I'm going to look at that picture of the relay'* in the thread you kinda followed to see which ones are in that vicinity.