Main Monitors

To meet OBD II requirements, the on-board diagnostic system must monitor the rationality of input signals and the functionality of output responses that can have an effect on vehicle emissions. In addition, there are several "main monitors" that review the result of system operations and their effect on emissions. The main monitors are as follows:

^ Catalyst
^ Fuel System
^ Misfire
^ Oxygen Sensor
^ Exhaust Gas Recirculation
^ Secondary Air Injection

Each of the main monitors is listed below with a brief background explanation and a description of how the monitor operates. Also, a list of the enabling, pending, conflict, and suspend conditions is included. Following these conditions is the diagnostic trouble code (DTC) produced by the monitor, the DTC flash code number and a number, referred to as a "SAE J2012", or "P" code. SAE J2012 codes are required by law for use with generic diagnostic scan tools. Finally, each section contains a list of the components that could possibly cause the monitor to fail.