Common OBD II Terms: Diagnostic

When used as a noun, the word diagnostic refers to any on-board test run by the vehicle's Diagnostic Management System. A diagnostic is simply a test run on a system or component to determine if the system or component is operating according to specification. There are many diagnostics, shown in the following list:

• Misfire
• Oxygen Sensors (O2S)
• Heated Oxygen Sensor (HO2S)
• Exhaust Gas Recirculation (EGR)
• Catalyst monitoring