Passive and Active Diagnostic Tests

A passive test is a diagnostic test which simply monitors a vehicle system or component. Conversely, an active test, actually takes some sort of action when performing diagnostic functions, often in response to a failed passive test. For example, EGR diagnostic active test will force EGR valve open during closed throttle decel and/or force EGR valve closed during a steady state. Either action should result in a change in manifold pressure.