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 databases, 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).