that isn't what I asked.

He states that
If it shorted to ground internally, the voltage I read would go to 0v, which would never happen normally, so I can turn the fan on. If it failed open (same as unplugging it), the voltage would go high, which would also never happen normally, so I again can turn the fan on.

so, I infer that if it went to ground, it would show infinte resistance, giving him a return of 0 volts.

which would work for the ground check instead of a sensor.

however, the problem occurs when the ground goes away, ie open circuit.
This too would trip the fan on due to the returning 12 volts.
which is why there needs to be a switch to determin if you are reading from a sensor or a ground.

IF I understood correctly.