OBD I vs. OBD II

How is OBD II different from OBD I?

An earlier onboard monitor called OBD I was originally mandated by the California Air Resources Board (CARB) in 1988. OBD I is used mostly to monitor for shorted and open circuits in the engine management system.

OBD II goes well beyond OBD I. Think of it as Enhanced OBD I. OBD II is a more complete vehicle monitoring system designed to detect failures — and potential failures — responsible for increased vehicle harmful emissions.

This is all about emissions.