Malfunction Indicator Lamp: Description and Operation

Fig. 39 Check Engine Warning Light:

An emission control system malfunction indicator light ("CHECK ENGINE") has been installed on all Porsches including Canada vehicles (1991 California legislation).
This system is controlled by the electronic control unit (ECU) which illuminates the "CHECK ENGINE" light (Fig. 39.) when a fault in the emission control system is detected. To aid the mechanic in finding the faulty component, a self diagnostic feature is incorporated in the system. To extract and identify the "fault codes" in the system see DIAGNOSIS AND TESTING PROCEDURES.