I have a 2018 AWD tlx, I brought a car with a front right damage and it was fixed, but always I have 3 codes , ACC, line departure and collision mitigation system, I never change the radar sensor because look good My question is how to know yf the sensor is good or only in the dealer figure this when they doing the calibration for the radar

 

The radar (if not damaged) may be out of alignment. You need to read the codes to determine what the issue is. I would take it to the dealer to get a proper diagnosis, but there is a risk that the dealer will try to push you to replace the radar (even if not damage)...