This student guide is for Unit 6, Emission Control Systems, in the Engine Tune-Up Service portion of the Automotive Mechanics Curriculum. It deals with inspecting, testing, and servicing an emission control system. A companion review exercise book and posttests are available separately as CE 031 221-222. An introduction tells how this unit fits into the total tune-up service, defines new terms, and provides work activities on the introductory information. Seven performance objectives are covered: perform operational inspections of positive crankcase ventilation system; perform operational inspection of fuel evaporative emission control systems; inspect, test, and service thermostatic air cleaner systems; inspect, test, and service air injection systems; inspect, test, and service exhaust gas recirculation systems; inspect, test, and service ignition timing control systems; and test exhaust performance, using hydrocarbon-carbon monoxide tester. Each objective is addressed in a separate section that includes these materials: introduction to the performance objective, performance checklist, list of tools and equipment needed to do the work activities for this performance objective, reading list, information sheets, and work activities that give hands-on practice in doing one part of the performance objective. (YLB)