System Description

OBD II stands for On Board Diagnostics II, the latest evolution of on vehicle emissions diagnostics that began on Chrysler vehicles with OBD I. OBD II was developed to allow Chrysler vehicles to meet the requirements of the Federal Clean Air Act and California Air Resources Board (CARB) legislation.

It is impractical (and very expensive) to provide every vehicle on the road with the equipment necessary to measure emissions of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx). Instead, the proven emissions and powertrain control devices available for these vehicles are checked for proper operation.

Malfunction Indicator Lamp (MIL):

The above legislation requires that the driver be informed when an emissions related system or component malfunctions or deteriorates to the extent that vehicle emissions exceed certain thresholds. To do this, the malfunction indicator or CHECK ENGINE light on the instrument panel is illuminated. The law states that the Malfunction Indicator Light (MIL) must be illuminated no later than the end of a second consecutive trip in which a failure of this type is observed, and illuminated immediately if catalyst damage is about to occur due to engine misfire.

In addition to illuminating the MIL, a diagnostic trouble code (DTC) is stored in the Powertrain Control Module (PCM), and can be retrieved by a service technician using a diagnostic scan tool.

To meet the requirements, the following systems must be monitored:

^ Catalyst
^ Fuel System
^ Misfire
^ Oxygen Sensor and Oxygen Sensor Heater
^ Evaporative System (Purge)
^ Exhaust Gas Recirculation (EGR)
^ Secondary Air Injection Systems
^ Any other input or output component that can affect emissions

You may be familiar with the monitors available on the DRB diagnostic scan tools. They allow you to monitor the operating conditions of vehicle components. The OBD II system monitors are different. They are checks made by the PCM's software to determine not only if these specific systems are operating, but whether they are operating within pre-established limits. While OBD I tests measure a component's electrical operation, OBD II monitors check a system's performance.