greeting everyone, i have a 03 monte with a 3400. 150k. runs fine. yesterday i noticed that my temp gauge is rising at idle. normally it runs 1 bar under the half way mark. after investigating, i realized that the cooling fans were not coming on. i did a series of tests. all three relays work . the temp gauge works as normal so im guess it it operating as normal. the fans dont come on when the ac is on either. i am getting power to the fans . jumped the fans with 12+ and neg they both blow strong. i do not seem to be getting ground to the fans, maybe the pcm? i grounded the fan to the engine and the fan for the ac worked as normal with the external ground but when i removed the ground the fan stopped. so , do i assume the pcm is not supplying a ground to the fans? or is my temp sensor malfunctioning? please help if you have expeirenced this problem thanks terry

 

Both fans not working? I wouldn't suspect the PCM. I think that the first job would be to check the temp sensor as you mentioned.

Seems to me that you have done a good job beginning to narrow down the problem.

I'm not positive, but I don't think that the PCM has a circuit that controls off/on of the booster fan or either of them for that matter. I can't see it in the HVAC schematics.

Coolant temp sensor says "hey, it's getting hot! Kick in the booster!"

PCM does control the a/c relay clutch but that booster fan will kick in even if the a/c isn't activated depending on the circumstances.

Hopefully, it's the TS and not a faulty ground.

 

where u live,is it warm? the temp is to be expected to rise while idling. the fans wont kick on till the temp gauge reaches above more than half way.

 

Along with the temp sensor, you might want to check the t'stat.

Think I was looking at the wrong schematic. Those fan circuits do go through the BCM and PCM.

 

Did you ever figure out the problem with your fans? I am have a similar problem with my 2003 3.4L MC. I was able to get Fan#2 going (fan on driver's side) by chasing down a bad ground. The ground for the fans are in the wiring harness between the two headlights, they exit the harness and attach to a screw right next to the drivers side head light. So, the ground was fixed and now Fan#2 turns on when the A/C is on and will kick on if the a/c is off and the engine temp gets too high. My problem is Fan#1 does not turn on at all. I have replaced the ECT sensor, checked all fuses, replaced all three relays, and used a wire to jump Fan#1 at the relay to ensure it worked (it did). Can anyone help??

 

I have a 2006 LT and had the same problem but my relays were installed wrong by a shop before I owned it the relays in the 06 Monte plug in upside down the relays are a 3114 except a larger in the middle. New to Monte Carlos but not GM

 

mine never turned on until my tune tuned them in at 180? i believe i have the same car as you, just 04