2000 Toyota Other

I have a V6 automatic which started out with a O2 sensor being bad. Changed the O2 sensor and the code for it disappeared. But now I am getting a P0125 code, temperature issue. I changed the ECT and still fails. Going to change the thermostat, but wanted some additional help. Is the O2 circuit tied to the P0125 code or is this just a coincidence? Also where is the thermostat located? I traced the radiator hose back on the drivers side and foumd it goes to a metal tube into a housing. This looks like the thermostat housing but I also noticed a sensor on it. I am assuming it is the gauge sensor. My question is should I change the thermostat or could it be something else.
May 27, 2007.

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