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.