Passive and Active Diagnostic Tests

A passive test is a diagnostic test which simply monitors a vehicle system or a vehicle component. An active test actually takes some sort of action when the performing diagnostic functions. An active test is often in response to a failed passive test. For example, the Exhaust Gas Recirculation (EGR) diagnostic active test may force the EGR valve open during a closed throttle deceleration maneuver. Or the EGR diagnostic active test may force the EGR valve closed during a period of steady speed driving. Either action should result in a change in the manifold pressure.