The secondary air injection system (AIR) aids in the reduction of hydrocarbon emissions. During open-loop fuel control, air is injected into the exhaust stream for a specified amount of time. Heat generated from post-combustion oxidation helps the catalytic converter reach operating temperature sooner (referred to as converter light off). The following conditions determine pump operation:

A remotely mounted bleed-off valve releases vacuum in the AIR system. The valve is similar in construction and operation to the evaporative purge control solenoid. As the mass flow of the exhaust gases pass the injection piping, a venturi vacuum effect occurs. The vacuum is strong enough to hold the internal shut-off valve closed when the PCM commands the secondary air ON. An inline check valve prevents air from escaping through the bleed valve when the pump is commanded ON.

Check valves remain the same as those used in earlier AIR systems. The valves are made of heat and corrosion resistant material. Located in the AIR piping to each bank, check valves prevent exhaust backflow when AIR is commanded OFF or an exhaust backfire occurs.

AIR hoses are made of heat resistant, non-reinforced rubber. Clamps, designed for high temperature conditions, connect the hoses to the pump and check valve/pipe assemblies of each cylinder bank. The air injection pipes, connected to the exhaust manifolds, are high temperature, corrosion resistant stainless steel.

The secondary air injection reaction (AIR) system is controlled by the PCM (after PCM replacement the Air pump is not allowed to run until the mileage is greater than 10 miles). At start up, the PCM energizes the AIR system relay. Battery voltage is supplied to the AIR pump, and bleed-off valve until the system enters Closed Loop or for a maximum time of 70 seconds, witch ever occurs first. Air from a remotely mounted filter is drawn into the pump by centrifugal action, pressurized, and pumped through check valves into the exhaust stream. Without the bleed-off valve, a vacuum would build in the AIR hoses due to the venturi effect created as the exhaust gases flow past the injection piping. The vacuum is strong enough to hold the internal shut-off valve closed. To prevent this situation, the bleed-off valve vents the vacuum to atmosphere. An inline check valve prevents air from escaping through the bleed-off valve during injection. Check valves in the AIR piping to each cylinder bank prevent exhaust backflow when AIR is commanded OFF or an exhaust backfire occurs.

The PCM monitors the AIR system in two stages (Passive and Active). The PCM initiates a two part Passive Test once each ignition cycle. Part one monitors the HO2S response when the PCM commands the air pump ON. If the HO2S remains proportionally lean (low HO2S signal), Passive Test 1 passes and Passive Test 2 is initiated. The Passive Test 2 monitors the transition from open loop to closed loop fueling. When air injection to the exhaust is commanded OFF, the PCM monitors the HO2S response. If the HO2S signal switches from a lean to rich condition for a specific amount of time, part two passes. If part one and part two pass, further monitoring of the AIR system is discontinued. If any portion of the Passive Test fails, the PCM initiates the Active Test. To run the Active Test, the AIR pump is commanded ON during warmed-up, closed loop operation. The PCM monitors the HO2S and long and short term fuel trim value response to air injection. If the HO2S signal remains proportionally lean for a specific amount of time (low HO2S signal) or the short term fuel trim values increase, the active test passes. If both HO2S1 signal and short term fuel trim values do not respond to air injection, the active test fails. If the PCM detects a consecutive number of active test failures, DTC P0410 will set. If a successful test occurs during the active test stage, a pass indication results and the test will not run until the next ignition cycle. Conditions for setting the AIR system fault:

If, during open loop fuel control, air injection is not present in the exhaust stream, high first and second hydrocarbon emissions result.

Continuous air injection to the exhaust stream will result in the following conditions:

No air injection to the exhaust stream will result in the following conditions:

The powertrain control module (PCM) monitors the secondary air injection reaction (AIR) system. A system malfunction will set DTC P0410.