Air Injection Pumps & Components

The Secondary Air Injection System, also known as the Air Injection Reactor (AIR) system, pumps fresh air into the exhaust system to cause further oxidation of unburned fuel in the exhaust, reducing Hydrocarbons (HC) and Carbon Monoxide (CO) emissions. The system includes an electric or belt-driven air pump, an air control valve, a vacuum switch, a diverter valve, one-way check valves, and hoses and tubing.

Pressurized air is generated by the air pump and fed into the exhaust system near the exhaust ports (in the cylinder head or the exhaust manifold) and at the catalytic converter, but not at the same time. The air control valve routes air to the head/manifold when the engine is warming up, to reduce emissions from the rich air/fuel mixture needed for a cold engine, and to heat the exhaust to bring the oxygen (O2) sensor and catalytic converter up to temperature sooner. When normal operating temperature is reached, the vacuum switch signals the air control valve to route air to the catalytic converter, where the injected air helps with the oxidation of HC and CO.

During deceleration, the closed throttle causes a rich air/fuel mixture. If air was injected into this mixture, a potentially component damaging backfire or explosion could result. To prevent this, a vacuum signal directs the diverter valve to route the compressed air to atmosphere during deceleration. The one-way check valves prevent hot exhaust gas from entering and damaging the air pump. These valves are located before the exhaust manifold and before the catalytic converter. When air is supplied to the component behind the valve, the exhaust manifold for example, the valve opens under the air pressure. When air is routed to the catalytic converter, the check valve closes in response to exhaust backpressure.

Although system diagnostics will vary according to make and model year, certain inspections are universal. Check the hoses and one-way check valves for evidence of burning, which can result in exhaust leaks and exhaust entering the system. On many air pumps, there is a centrifugal filter behind the pulley that can be replaced. Most modern systems will set Diagnostic Trouble Codes (DTCs) in the Engine Control Module (ECM) if there is a problem in the system. If air is not pumped to the head/manifold during warm-up, there will be excessive emissions and reduced fuel economy. Correspondingly, if air is pumped to the head/manifold when the engine is at normal operating temperature, the excess air in the system will be interpreted by the O2 sensor as a lean condition. In response, the ECM will create a rich/air fuel mixture, reducing fuel economy and causing the vehicle to fail an emissions test.