While I was scanning the codes on my truck, we did realtime water temp and was wondering if the temp shown is from the ECU sensor for water temp or the gauge sensor? I'm sure its ECU sensor, but I just want to make sure.

 

there are 2 sensors as you note. One runs directly to the gauge on the dash and has no connection to the PCM (ECU for you). It is just the closed loop display just like the oil pressure gauge. The other runs to the PCM and this is what you were reading on the scanner.