I solved the problem myself. Everything happened upon returning from Greece to Romania. The first time the needle from the engine tachometer fell, then 2 days later the water thermostat needle also fell and in addition I got the error that the antifreeze temperature was high and the engine goes into protection and stops. When you put the tester on the car, it gave me the following errors, U1601 on the engine, U1701 on the trip computer, these mean a communication error on the engine node. Plus another low oil pressure error.
I will explain how I solved the problem. The first time I changed the oil pressure sensor and the low oil pressure error went away, the other U1601 and U1701 still remained plus the one with high antifreeze temperature and engine shutdown. Later, on the advice of a Fiat mechanic, I doubled the ground cables. The errors have not disappeared even now. Then I noticed that the battery was not good, it had no more amperage and could not start the engine and I changed it. Even now the errors have not been resolved. Then I noticed that the alternator with the consumers on only compensates up to 12.2 volts with the engine at 2000 revolutions. I also changed the alternator and it still hasn't been solved. I then borrowed the dashboard clocks thinking I had broken clocks. In the same way, the same errors were not resolved even with the changed clocks. Next, the U1601 on the engine ecu and U1701 on the computer board errors and the increased antifreeze temperature error did not go away, plus my tachometer and antifreeze temperature were dropping needles. Then I changed the crankshaft speed sensor and in vain. I sat and thought more and changed the thermostat. Now after changing it, the water temperature rise warning is no longer displayed, but still the clocks kept falling, the water clock and the tachometer . After this, I saw some videos on some Russian sites about the loss of connection to the Fiat Stilo on the canbus network, but which gave similar errors depending on what equipment the car had, abs, steering column and so on. I will continue in the next post.