There are two primary types of on-board diagnostic codes: generic (or universal) and manufacturer-specific. The first digit of an OBD code specifies the related system: powertrain, body, chassis or undefined. The second digit states whether the code is generic or manufacturer-specific. The last three digits specify the issue itself.
The OBD system was designed to standardize the process of troubleshooting between all vehicles. All vehicles made after 1996 are required to have a standardized on-board diagnostics port and use the OBD code format. Common components, such as gas caps or oxygen sensors, utilize the generic codes, while components unique to a certain vehicle or manufacturer use the manufacturer-specific codes.