The coolant temperature sensor on the wet thermostat is to send temperature information to the engine ecu . the engine ecu decides IF the fan should be on and activates relays to power the plug at the bottom of the fan shroud ,
that plug is a fan speed resistor , depending on how hot then rad is ,the resistor pack will turn on the fan and control it's speed ,and send info back to the ecu to say what speed etc
you'd need to back probe that plug with power to the L+ and N- which is best done fan removed (because it's a pig to reach and it will probably bring the fan on ,which will eat any fingers etc anywhere near it , so be careful
re the relays , one failing will stop the fan working , as will any blown fuse in the circuit , it's not a back up relay system .
also in live data you could check fan control 1, 2 and 3 (active or inactive) radiator coolant temperature voltage and temp reading when warm etc
also also with the
codereader
you can do output tests to check fan and blower motors
also also also
did you confirm that the car has NO aircon ? and never has
I.E compressor,condenser,front rad fan not present