2006 Chevy Equinox Cooling Fan Issue

Hello, Here is a mystery for someone. I have a 2006 Chevy Equinox that developed a cooling fan issue. Here is the problem. The fans stopped working resulting in the car overheating in the Florida summers. It was not an issue if I was driving but stopping at a stoplight the temp would start to rise. I found the fans were not coming on.

Here is what has been done. The fan assembly was replaced. Then the fuse box, the fuses, relays and the pig-tale cable. All of this and there is still a fan issue.

Three different mechanics tell me it is not the PCM "Power Control Module" But they cannot seem to isolate the problem. What makes it worse is it becomes intermittent.

Now here is my test. I have attached the wiring diagram. I find that if I open the top of the relay and manually close the relay the fan comes on. Depending on the relay. There is two relays. One for High Speed Fan (the big fan) and one for the low speed fan (Small fan). So I can manually close the relays and the fans operate. This would indicate that the Fans, fuses, and relays are working. I then tested and I have a constant +12 volts all the time applied to the relays. Even if the car it turned off. This is normal. I then find that if I supply ground -12 volt to the relay the relay closes and works. The -12 volt (ground) is provided by the PCM "Power Control Module".

My questions are as follows;
What controls the PCM (Power Control Module)?
Could the temperature sensor be defective even though the temperature gauge in the dash is working correctly? Could the PCM not be getting information from the temperature sensor?

Now more information. The Florida temps have cooled off so the car is not overheating but runs above normal to about half way when stopped at a traffic light.

More important information. The large fan works if the AC is on. So if the temp starts going up at a traffic light I turn on the AC and the large fan comes on.

So something is not telling the PCM to supply ground to the fan relays resulting in the fans not coming on.

I am unable to find any information on my car on the internet as to how a PCM works and what controls the PCM.

Any suggestions is greatly appreciated.

There may be two temp sensors, one for dash and one for PCM-a scan tool will tell you right away if PCM is seeing correct temp.- but...

How do you define "overheating" - I define it as boiling over- puking its guts out- but some think that 3/4 way to red is overheating. Cars wait until about 227 degf to turn on lo fan and 238 degf or so to turn on hi speed fan.

If yours is not spewing coolant- then read on...

This problem only exists when weather is cool enough NOT to run a/c- people go nuts because their gage runs "warmer than usual" - of course it does- usual is a/c on where fans are needed for condenser (a/c) only. Without a/c I thoroughly expect to see warmer than usual- until the fan(s) come on at their intended temps.

To test- let idle for extended period with scan tool attached (your ace mechanics can do this) - watch PCM coolant temp- put a blanket over hood if needed and see if fan(s) come on at 227+ degf. Do NOT worry about dash temp gage- it will climb "higher than usual" and can be quite alright- until fans come on.

I have seen this complaint numerous times, and it is all in the interpretation and definition of "Overheating"