Computers and Control Systems: Description and Operation

Fig. 1 Closed loop emission control system electrical diagram:

The Closed Loop Emission Control System, Fig. 1, precisely controls the air/fuel ratio, allowing the use of a three-way catalyst to reduce oxides of nitrogen, hydrocarbons and carbon monoxide. The major components of this system are the oxygen sensor, electronic control module (ECM), controlled air/fuel ratio carburetor and a three-way catalytic converter. This system utilizes a dashboard mounted malfunction indicator lamp which, for some failure modes, will inform the driver of the need for unscheduled maintenance. In the event of system malfunction the ``Check Engine'' light will come on and remain on as long as the fault occurs and the engine is operating. The electronic control module incorporates a diagnostic program which will assist in diagnosing closed loop control system malfunctions. When activated, the diagnostic program will flash a code through the ``Check Engine'' light which isolates the source of the system malfunction.