How do you know when your "Cam Shalf Sensor" is malfunctioning on a 89 Buick leSabre?

I recently got the code 41 on my car and it was code 41 but the car starts on a dime and runs great,tell me what may the problem why that code came up?How do you know when your "Cam Shalf Sensor" is malfunctioning on a 89 Buick leSabre?the magnet on the cam gear fell off. That happens all the time on this engine. Shouldn't be a problem if you don't mind the check engine light on all the time.