the PCM isnt related to the voltage regulator in the alternator. the PCM is the Power Control Module. it controls all the spark, fuel, and other settings that allow the car to run.
to check the voltage regulator get a volt meter and first test the battery with the car off so you know the voltage out put. then start the car and check it again. if it is changing more then one volt then you have a prob out put should be about 13.5 volt IIRC. anything below this could cause a problem light you are describing