Hey guys this just started happening. When the car is not moving it will heat up and the fan will never turn on. I ran 12v to the fan and it turned on and had tons of power, so it's not the fan. I checked the big fuse under the dash and it was good. I also swapped the relay under the hood with the heater relay and no difference. It does not come on with the AC on either. I then replaced the coolant temp sensor that's on the thermostat housing and that didn't fix it. I then unplugged the coolant temp sensor while the motor was running. It threw a CEL and the fan came on. since the CEL is on from me doing that the fan runs continuously. What else could it be guys? I'm assuming when I reset the computer tomorrow to turn off the CEL the fan will go back to not working. What can I test? Thanks in advance

 

I think there's also a coolant temp sensor on the radiator and that's the one that controls the cooling fan. The temp sensor on the thermostat housing is for the temp gauge in the instrument cluster. Check to see if there's another sensor on the radiator, if not it could possibly be an issue with the pcm.

 

Are you sure it is overheating? Dual fans? With a/c on does one of the fans come on? Without the a/c on, and not hot dosen't mean the primary fan should be on.

 

It only has one fan. It get about 3/4 of the way to the red on the meter. I also heard that there were two sensors. Can someone confirm this? Also the fan dosent come on when i turn the AC on. Thanks

 

does it have a/c? With the a/c on, does the fan come on? You said you disconnected the temp sensor, and fan came on, that is a fail safe system. Having two sensors I don't think so, but it is pointing to that.

 

Yes it has AC and no it does not turn in with the AC on.

 

I don't know. If the sensor is a thermocouple, that would explain both things. Opening the circuit will read infinity on a thermocouple, in other words it will read max, and that would explain why the fan came on when unpluged. If the sensor (thermocouple) is shorted, that would explain why it isn't comming on as it is sending an indication that it isn't hot. What I don't understand is the guage reading, unless there are two sensors, one for the gauge, and one for control.

 

what year cav?
Most cooling fans are ecm controlled. the fan should turn on at 223' F. The ecm should also turn the fan on when ever the compressor clutch is engaged.

the fact that the fans runs when the ect is unplugged tells me that the wiring and fan are ok.

So the question is:
Is their an overheat condition? What temp is it getting to? use a scan tool and read it live.

Does the A/C compressor cycle on? A/c systems will overpressure in a mattter of seconds and shut down with no fan operation.

 

its a 96'. i have not plugged it into a scan tool to measure the actual temperature. I mean maybe it is never hitting the temp to turn the fan on, but im not sure.

 

is the temp warning indicator coming on?

does the A/C even work?