During a car wash, the passenger wiper arm assembly broke off the vehicle. The break happened to the thick cast metal portion of the arm that connects to the rotating shaft on the vehicle and was broken at an angle across the entire part. This is the most substantial part of the arm assembly. The metal part that failed appeared to be made of cast pot metal and the break showed a grainy coarseness as if it were broken glass. The rest of the arm assembly appeared to be undamaged, as was the wiper blade assembly.