See Figures 1 and 2
Two different feedback systems are used with 1981 and later Jeep vehicles. One, the C4 system is used with 4-151 engines built for sale in California. The other, the Computerized Emission Control (CEC) System is used on 6-258 engines built for sale in California. Each system is designed for the same purpose, to reduce exhaust emission using a Three-Way Catalytic Converter (TWC).
Each system is computerized, utilizing microprocessors, and each is highly complex, requiring professional service. Therefore, no service procedures are given in this guide for the diagnosis or repair of these systems.