Air Injection: Testing and Inspection

FUNCTIONAL TEST
Functional testing of the secondary air injection system is part of the On-Board Diagnostics system.

FLOW TEST
During the flow test, oxygen sensor control is switched OFF (engine operates in rich condition during this time). At the same time, the secondary air injection pump is switched ON. This means that fresh air is supplied to the exhaust manifold which increases the oxygen percentage in the exhaust. The oxygen sensor now measures a lean mixture. To pass the test, the oxygen sensor must experience a lean mixture over a certain length of time, meaning that the secondary air injection system supplies sufficient air quantity to achieve this condition.

LEAK TEST
The requirement for this test is first passing the flow test. With the engine warm, the secondary air injection pump is switched on during idle. However, the combination valves are not triggered by the secondary air injection valve, i.e. they remain closed. When the secondary air injection pump is switched ON, oxygen sensor control of the ECM is observed. If there are no leaks in the system, no fresh air can get into the exhaust manifold. Oxygen sensor control must not react (causing a rich or lean condition). On the other hand, if this system is leaking, oxygen sensor control must react to the mixture that is now lean (because of excess oxygen in the secondary air injection system) with definite richening which is recognized by the ECM.