Engine Control Module: Description and Operation

SELF-DIAGNOSIS
The ECM monitor the input/output signals (some signals at all times and the others under specified conditions). When the ECM detects that an irregularity, it memorizes the diagnostic trouble code, and outputs the signal to the self-diagnosis output terminal. The diagnosis results can be read out Scan Tool (ST). Diagnostic trouble code (DTC) will remain in the ECM as long as battery power is maintained. The diagnostic trouble code will, however, be erased when the battery terminal or the engine control module (ECM) connector is disconnected or erased by Generic Scan Tool.