Thread: Cooling Fans not kicking on.

Okay, I'm new to the site, so here's my first post. I have a 1997 Grand Prix GT and just recently, my gf just bought a 2000 model Grand Prix GT. On the 2000 Model Grand Prix GT, her fans are not kicking on. See, I first replaced the CTS sensor due to a engine code. Now, the engine gets really hot fast and the fans never kick on. I turn the A/C on and the fans don't kick on either, so I'm wondering...do I have a new bad CTS sensor? I never checked the fans when we got it a couple of day ago and it's been on the road most of the way.

And BTW, I already replaced the thermostat too. I checked the new thermostat by placing it in boiling water to make sure it opened up. And it did of course. Is there a way I can check both fans by hooking up a 12V supply or grounding a certain wire? Any help would be appreciated.

check the relay and fuse

Okay, I just went outside, disconnected the leads to both fans and was able to apply voltage to my fans. Both worked fine. I'm just wondering if the computer is messed up or did I just get a bad CTS sensor from the parts store. I'm going to do a little more searching on the site for wiring diagrams, but if anyone knows of any quick way to test the relays or a signal from the computer, I'd appreciate it.

******* Problem Fixed ********

Okay, here's the deal. Don't buy anything electrical or electronic from Autozone. Here's what I did. I hooked up a laptop, scanning software and an obd2 interface. I watched the coolant temp and the gauge. The gauge started climbing drastically compared to the coolant temp from the PCM side. For example, the temperature gauge was reading 200 degrees, but the car was only reading 120 degrees. Then when the gauge was 240 degrees, the PCM was reporting only 170 degrees. Finally the car got around 196 degrees, the gauge on my dash was reading 260 degrees! So of course, I was thinking the fans never kicked on when in reality, the PCM never got to 212 degrees for the fans to operate. I also know that when operating the air conditioner, the fans don't kick on immediately like previous cars.

I went to O'Reilly's and purchased a Borg Warner CTS sensor and replaced the one I got from Autozone. Now, I fired up the laptop and watched both the gauge and PCM coolant temp and guess what, they both were reading more accurately. Now, I got the car to 212 degrees, and the fans DID kick on. So in reality, the car was never overheating, the CTS sensor was bad causing the temperature gauge to climb to fast!

Anyway, what an experience. Oh well, the car is happy and so am I.

Great info!

I have the same problem - although I only have a 30F/49F differential.

But... how do you manage that sensor change-out? It looks to be pretty difficult to get at in my 1999 GT and wonder if/how some coolant has to be drained?

I took the motor mount off on the side where the sensor was. Then took the thermostat housing/neck off and left the upper hose connected to it. Once it was maneuvered out of the way, there was another bracket I had to take loose. I remember three bolts, where I took two of them out and loosened the third one so I could swing that bracket to make more room to get to it. Now, I didn't drain my coolant out. I lost a little taking the thermostat neck/housing off. Then when I actually could turn the sensor by hand, with a latex glove, I just put my finger in the hole of the sensor while someone handed me the new sensor. That way I didn't loose as much coolant. Overall, it took about an hour to do all this including hunting for wrenches, etc. Good luck with it.

Picked up one of those Borg Warner sensors and noticed that it doesn't include any thread sealant or gasket. Do you recall if the original equipment sensor did?

Just don't want to deal with any post installation leaks if you know what I mean...

Mine had the red sealant on my sensor, but go ahead and get some pipe thread tape.

Very well.. thanks for the update.

I have 1996 grand prix v6 3.1 - 2nd fan does not work but i manually tested it and works fine. replaced the relay - still will not work - is it the temp sensor and where is that located?

I don't know much about the 3.1L V6, but the temp sensor should be located close to the thermostat housing or around about. Now, I do know that some cars don't kick on the second fan until the temperature get's over 230* F. I don't have a wiring diagram for that car, but you might want to look around to get one to see what conditions the secondary fan will turn on.

Hey, i have a 2000 grand prix SE and the temp guage is climbing well over 100 degree's does it need to get to a specific temp before the fabs kick on because mine are not and runs anywhere from 100 to 200 degrees