This SAE Recommended Practice is applicable to all light duty and medium duty passenger vehicles and trucks with feedback fuel control system. Specific applications of this document include diagnostic, service and repair manuals, repair data bases, and off-board readout devices. This document focuses on a diagnostic code format and code messages for automotive electronic control systems. The use and appropriate updating of this document is strongly encouraged; however, this document does not prohibit the use of additional codes for additional diagnostics. This document is applicable to all light-duty gasoline and diesel vehicles (LDV and LDDV), light-duty gasoline and diesel trucks (LDT and LDDT), and medium-duty gasoline vehicles (MDGV).