Secondary Air Injection System Description
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Secondary Air Injection System Description
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The Secondary Air Injection (AIR) system helps reduce Hydrocarbon (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx) exhaust emissions. It also heats up the warm up 3-way catalytic converters quickly on engine start-up so conversion of exhaust gases can occur sooner.
Air Pump
The AIR pump is mounted to the front lower center of the engine and supplies the air to the AIR system. The electric air pump pressurizes fresh air and pumps it to the check valve near the front exhaust manifold. Air is directed to the exhaust manifold, which distributes the air to the respective exhaust port. The air is led via short ducts in the cylinder heads. These ducts lead into the respective exhaust port. The AIR pump is controlled by the ECM. Battery voltage to the AIR pump is controlled by the AIR pump relay. When the ECM provides a ground circuit for the secondary AIR pump relay, battery voltage is allowed to power up the AIR pump.
AIR Pump Relay
The AIR pump relay supplies high current and battery voltage to the AIR pump. The ECM commands the relay ON by supplying a ground to the relay control circuit.
AIR Pressure Sensor
An AIR system pressure sensor is used to monitor the air flow from the AIR pump. The engine control module (ECM) supplies 5 volts to the 5-volt reference circuit and supplies a ground to the low reference circuit. The sensor provides a signal voltage to the ECM relative to the pressure changes within the AIR system.
AIR Check Valve
In order to avoid exhaust gases leaking back through the secondary air system there is a check valve in the system. Air is allowed to flow from the secondary air injection pump to the exhaust manifold but exhaust gases are not allowed to flow towards the pump. The check valves prevent back flow of exhaust gases into the AIR system in the event of an exhaust backfire.
AIR Pipes and Hoses
The AIR system hose carries filtered air from the engine air cleaner to the AIR pump inlet. The pipe/hoses carry the air from the AIR pump to the exhaust manifold.
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Results of Incorrect Operation
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The ECM monitors the secondary air injection (AIR) system for faults during cold start-up operation. When the system's pressure or relay circuits operations vary too far from the predicted values, a DTC will set. Diagnostics detect the following conditions:
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A partially blocked or leaking AIR system
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A malfunctioning AIR pump
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A malfunctioning AIR check valve
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A malfunctioning AIR pressure sensor
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A restricted exhaust system, forward of the catalytic converter
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A malfunctioning AIR pump relay
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