Passive and Active Diagnostic Tests

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