Closed Loop Emission System
A CHECK ENGINE light is used to inform driver of unscheduled maintenance problems within vehicle computerized engine control system and to aid technician in diagnosing self-diagnostic system. See CHECK ENGINE LIGHT under SELF DIAGNOSTIC SYSTEM in this article.
The closed loop emission system controls air/fuel ratio to reduce emissions and improve driveability. SeeFig 1 . Input devices provide signals to Electronic Control Module (ECM). The ECM processes information from input devices and sends output signals to various devices. See INPUT DEVICES and OUTPUT SIGNALS.