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 as shown in following list:

• Misfire.
• Oxygen sensors.
• Oxygen sensor heaters.
• EGR.
• Catalyst monitoring.