If feedback system consist of variable resistor, then all the sensors works plus you don’t see any trouble code but if feedback system consist of O2 sensor even then every sensor works but you get out of specs reading from O2 sensor and correspondingly LTFT, STFT shows out of spec values that’s why you see a trouble code light.
if wiring connections from Emulator/advancer is made with O2 sensor then it fools ECU that system is working fine even though voltage from O2 sensor is out of spec which is then manipulated by emulator and sends a different signal to ECU so that it thinks every thing is working fine and in return you dont see a trouble code.