radiator fan control wires

Hello,
after searching a lot for informations about how the (two) fan control wires coming from the ecu start/stop the fan and change the fan speed,
i got this information from a garage owner:

- the first wire must bring 12V, when the ignition key is turned
- the second wire brings the start/stop/speed command, you cannot see the command with a multimeter, you need an oscilloscope

I write this post to share with this forum this information,
and to ask if someone do agree with what the garage owner says,
or has different informations.

Let me know

Thank you!

UPDATE:

I changed the fan, as suggested, and it works,
i tried it with with actuator test
Lexia has cancelled the error.