OBD I, OBD II And Engine Manufacturer Diagnostics (EMD) Overview

The California Air Resources Board (CARB) began regulating OBD systems for vehicles sold in California beginning with the 1988 model year. The initial requirements, known as OBD I, required identifying the likely area of concern with regard to the fuel metering system, exhaust gas recirculation (EGR) system, emission related components and the PCM. A malfunction indicator lamp (MIL) was required to illuminate and alert the driver of the concern and the need to repair the emission control system. A DTC was required to assist in identifying the system or component associated with the concern.

Starting with the 1994 model year, both CARB and the Environmental Protection Agency (EPA) mandated enhanced OBD systems, commonly known as OBD II. The objectives of the OBD II system are to improve air quality by reducing high in use emissions caused by emission related concerns, reducing the time between the occurrence of a concern and its detection and repair, and assisting in the diagnosis and repair of emission related problems.