ACC/ PAS UNAVAILABLE WARNING: APPROXIMATELY EIGHT MONTHS AGO WHILE DRIVING ON A CITY STREET IN SARASOTA, FL THE PAS SYSTEM WAS ACTIVATED AND ABRUPTLY STOPPED MY VEHICLE WITHOUT REASON. ON TWO SEPARATE OCCASIONS THE "ACC/PAS IS UNAVAILABLE" WARNING HAS APPEARED ON MY INSTRUMENT PANEL. ON THE FIRST OCCASION, A VEHICLE TO MY LEFT WAS ATTEMPTING TO MERGE INTO MY LANE OF TRAFFIC WHILE WE WERE APPROACHING AN INTERSECTION ON A CITY STREET. I ATTEMPTED TO HONK MY HORN (WHICH FAILED MAKING AN AUDIBLE SOUND) AND SWERVED TO PREVENT THIS IMPENDING COLLISION. THE DRIVER OF THE VEHICLE IN FRONT OF ME ALSO WITNESSED WHAT WAS OCCURRING AND SLAMMED ON THEIR BREAKS. MY PAS SYSTEM FAILED TO ALERT AND APPLY PRESSURE AND/OR STOP THE BREAKS AS THIS SAFETY FEATURE IS DESIGNED. DESPITE MY EFFORTS TO BREAK QUICKLY THE VEHICLE IN FRONT OF ME AND I COLLIDED. THE FIRST DRIVER THAT MERGED INTO MY LANE FLED THE SCENE. THERE WAS NO DAMAGE TO THE VEHICLE IN FRONT OF ME AND THE PORSCHE HAD MODERATE FRONT END DAMAGE. A POLICE REPORT WAS FILED. THE VEHICLE WAS TAKEN TO OUR INSURANCE COMPANY'S AUTO REPAIR EXPRESS PROGRAM AT A COLLISION CENTER OF THEIR CHOICE. IT WAS THEN SENT TO OUR LOCAL PORSCHE SERVICE DEPARTMENT FOR INSPECTION AND REINSTALLATION AND CALIBRATION OF THE PAS CAMERAS AND OPERATIONS. ON THE SECOND OCCASION APPROXIMATELY 10 DAYS AFTER HAVING THE VEHICLE BACK FROM THE BODY SHOP AND INSPECTIONS, I WAS SITTING AT RED TRAFFIC LIGHT ON A CITY STREET. THE LIGHT CHANGED GREEN, CARS BEHIND ME S