Strange Fan / Overheat Issue
I am hoping someone here has a better understanding of the cooling system wiring than I do. I have a strange problem with my fan. It runs on high and low speed when the AC is on, but when it is off, nothing. It will overheat and report 212 coolant temp on the DTC scanner. This thing has 4 coolant temp sensors in various places. I read that the one on the radiator "controls the fans". I am not sure what that means because all the inputs go to the ECU and it is reporting 212. The sensor is reported to the scan tool is the one on the plastic thermostat manifold. I have connected a 150 ohm resistor to it and it will report 231 and then turn on the fan and create a trouble code - way too hot! I have also connected a resistor to the radiator sensor harness and nothing. I don't have any visibility to any of the sensors except the 1 that reports.
I have replaced the thermostat which was stuck closed, so the car definitely overheated at some point. The thermostat is working correctly and opens at around 200F.
So my question is, among the various temp sensors, what is the sequence, or which sensor is most important that the computer wants to turn on the fans and which sensor is most likely bad? Is there any way to look at all 4 sensors in the scan tool? I have replaced the thermostat sensor and will be replacing the radiator and engine block sensors. The only one I am not replacing is the thermostat manifold sensor that is reporting correctly.
If that doesn't work, I am going to replace the radiator sensor with a standard thermostatic switch and run it to the high speed relay.....
