This SAE Recommended Practice establishes a uniform practice for protecting vehicle components from "unauthorized" access through a vehicle data link connector (DLC). The document defines a security system for motor vehicle and tool manufacturers. It will provide flexibility to tailor systems to the security needs of the vehicle manufacturer. The vehicle modules addressed are those that are capable of having solid state memory contents accessed or altered through the data link connector. Improper memory content alteration could potentially damage the electronics or other vehicle modules; risk the vehicle compliance to government legislated requirements; or risk the vehicle manufacturer's security interests. This document does not imply that other security measures are not required nor possible.