Full [ high] fan is at 105 and is triggered by the thermistor sensors resistance value at thermo housing.. this triggers a
switching transistor circuit in the control unit which grounds the aux fan relay coil . [ thus, giving you high fan]. The control unit does not have to be on for this to work, the circuit is simply in the control circuitry...
To find out which is out of calibration, you have to test both the gauge sensor [ single wire sensor] and the aux fan sensor [ 2 wire] with an ohm meter and compare it to a temp/resistance chart.
I believe that chart is in the CD
If not, I have listed both somewhere in the archieves..
I would start with the gauge one first, just so you know where you are at , temp wise...