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Repair Topics > Computers and Sensors > Secondary Air System Monitor — I/M Secondary Air Monitor

Secondary Air System Monitor — I/M Secondary Air Monitor

Secondary Air System Monitor

Secondary air systems are used to jump start a cold catalytic converter and to cut down on cold start emissions. A catalytic converter must reach approximately 400° to 600°F in order to properly reduce emissions. When a cold engine is started, a large amount of fuel is unburned due to the “quench” effect of the cold combustion chamber and cylinder head. That unburned fuel then enters the cold catalytic converter where there’s not enough oxygen to burn it off. Lacking extra oxygen and heat, that raw fuel is sent out the tailpipe as pollutants.

How secondary air works

A secondary air system is designed to pump extra outside air directly into the catalytic converter to provide more oxygen to burn off the extra fuel and get the catalytic converter up to operating temperature much faster.

It uses an air pump and a series of valves that route the pumped air directly into the exhaust manifold or into the catalytic converter.

What the secondary air monitor checks

The Secondary Air System Monitor checks for component integrity and system operation, and tests for faults in the system. The computer runs this Monitor once per trip.

The Secondary Air System Monitor is a “Two-Trip” monitor. If a fault is found on the first trip, the computer temporarily saves this fault in its memory as a Pending Code. The computer does not command the MIL on at this time. If the fault is sensed again on the second trip, the computer commands the MIL “On,” and saves the code in its long-term memory.

©, 2022 Rick Muscoplat

Posted on by Rick Muscoplat

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