The CCS system is a combination of systems and calibrations. Many of these are not visible or serviceable, but are designed into the engine. Originally, in 1968-69, the system was comprised of special carburetion and distributor settings, higher engine operating temperatures and a thermostatically-controlled air cleaner. In later years, the Carburetor Heated Air (CHA) system was used independently of the other settings on some engines. Likewise, some engines used the special settings without CHA. In 1970, the Transmission Controlled Spark (TCS) system was incorporated; the system was renamed Computerized Emission Control (CEC) in 1971. The name reverted to TCS in 1972. In 1973, Exhaust Gas Recirculation (EGR) was also added to the system.