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Toyota Avalon heater sensor, PLEASE HELP

My 1996 Avalon has 245000mi it runs great except the radiator fans dont come on. If I unplug the drivers side top sensor, the fans come on, and stay on. I changed that one, but it didnt help. They say there are 4 sensors. Any suggs.

The information I found shows two ECT switches, and one ECT Sensor (Sender). ECT = Engine Coolant Temperature. The two ECT fan switches cause the radiator fans to come on at different temperatures (about 180F and 190F degrees). The ECT Sensor (Sender) sends its signal to the engine computer, and directly, or indirectly, to the dash temperature gauge.
The Haynes Repair Manual shows checking the ECT switches in a container of heated water (heated to various temperatures), with a multimeter (ohm meter). You need to do that, and check the wiring to the switches for shorts, or opens.

Thank you so much, I should have mentioned that the temp gauge on the dash “appears” to be working. It reads the normal range. I have a multi meter, how would I check the sensors with it, what should it read. Also I have only found three sensor like you stated, not four like others have told me.
Thanks Derek