On-Board Diagnostics: Notes

On-board diagnostics allow the Engine Control Module (ECM) to identify malfunctions and store them in memory in the form of Diagnostic Trouble Codes (DTC). DTCs are stored until memory is erased. Diagnostic data is transmitted between ECM and scan tool through the Data Link Connector (DLC). DLC is located behind cover under left side of steering column. DTC memory is part of permanent memory, and is not effected by loss of voltage supply. When DTC is stored in memory, ECM illuminates appropriate light in instrument cluster. DTCs recognized by ECM which would lead to higher emissions are indicated by Malfunction Indicator Light (MIL). DTCs recognized by ECM to be related to "E-gas" malfunctions, are indicated by Electronic Power Control (EPC) warning light.