Q: the high speed of coolant fan doesn't turn on when the engine overheats

its the opel astra G CD 2004 the car is a Brazilian made for Chevrolet (in Brazil called Chevrolet astra) but came to Egypt under the Opel name from the GM factory in Brazil with z16xe engine and an auto transmission with HSFI 2.1 ecu, it originally has an HSFI 2.3 ecu that came with the car from the factory, but it showed malfunctions and had to be replaced and HSFI 2.3 wasn't available later the ecu dropped signal to the fuel pump relay and the car wasnt able to start, the local mechanic repaired it by getting a separate 12v signal only when the ignition is on through a diode from a near by relay and the car was pumped back to life (this isnt the main problem but i wanted to denote a faulty ecu) now the ecu dropped signal of the high speed radiator fan so it would turn on but only on the low speed thus on daily use there is no overheating unless I open the A/C in traffic jams while on the highway it cools back can I check for wiring error at the relay box or change wiring or what?

My car has 7427871 miles.
My car has an automatic transmission.