Rad fans wont go on, but sensor and fans still work

[m1nd64m3]

My fans wont kick on even though the fan itself works(tested it). I would like to believe its the coolant temp sensor but on my logger it still reads the temperature. So what I would like to know is the coolant temp sensor what causes the fans to go on or does the ecu turn them on based on a temperature reading from the sensor?

I recently replaced the thermostat when I put a new motor in so that is not it either. Had the problem with new and old motor but same temperature sensor. I switched the relays around and still no luck with that either unless all my relays are bad, which I highly doubt.
I have searched around and still cannot get a definitive answer on weather its maybe an ecu problem or sensor.

 

[luv2rallye]

You do know that the temp gauge and ECU (which controls fans) have separate sensors I hope. They are both by the thermostat (radiator cap). The temp gauge is the one with 1 wire, the ECU one has 2 wires. Also note that turning on the A/C should force both fans on.

 

[Old Mitsu Tech]

You got it. If the fans come on by manually triggering, I would go with the fan switch.

Good Job

 

[m1nd64m3]

I see, my original thinking was the smaller one was for the gauge only and that the ecu read the temperature from the other sensor. I didnt know that sensor was basically just a switch for the fans. Thanks