Passive and Active Diagnostic Tests
WARNING: This page is about a different car, the 2002 Isuzu Rodeo Sport, 2002 Isuzu Rodeo, 2002 Isuzu Axiom, and 2002 Honda Passport. However, it is still accessible from the selected car via links, so may be relevant.
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.