Only 3 things that ecu logic uses to command fans on .
1 Coolant temp sensor (2 wire)
2 aircon switched on
3 ecu detected fault and running in safe mode .
could be as simple as ecu coolant sensor faulty or wiring faulty (if disconnected, open circuit or resistance always at hot water value fan always on) .
* this been connected right after engine fitting !? harness or other wirng damaged connected wrong !?
aircon fault or fan relay circuit fault, ecu control circuit fault .
Pretty easy test these circuits and narrow things down.
If you got consult adaptor you can see what ecu doing and what input value is switching the fans on.
Every owner should have the consult adaptor as was less than 20bucks and obd scan tech nissan software free (see useful link section)
simply testing pin 9 at ecu with DMM (ecu ground switch control for fan relay switch side) will tell you if ecu commanding fans on or if relay stuck on or grounded another way .
Simple checks on coolant sensor another good place start .
Some thread links below with pdf file links and general tips that could help you do diagnosis on this fault if read through them (if simply not wrong plug harness on ecu coolant sensor or similar) .https://www.gtir-motorsport-club.com/t6996-radiator-fans-refuse-to-kick-inhttps://www.gtir-motorsport-club.com/t6965-need-expert-advise-for-start-up-issues