Secondary Air Injection System

The Secondary Air Injection Reaction (AIR) system is designed on the 5.7L engine to lower the exhaust emission levels after engine start- up. The PCM commands the AIR pump relay ON by supplying a ground to the relay control circuit. This action energizes the AIR pump, which forces air (oxygen) into the exhaust stream. The PCM also commands the AIR vacuum solenoid valve ON by supplying a ground to the control circuit of the AIR solenoid. With the AIR solenoid activated, engine vacuum is then applied to the AIR shut-off valve. Fresh air from the AIR pump then enters into the exhaust stream. The air that is introduced into the exhaust system accelerates catalysts operation, reducing exhaust emission levels. When the AIR system is inactive, the AIR shut-off valve and check valves prevent airflow in either direction.

The system includes the following components:

• AIR Pump -
  
  The AIR pump supplies fresh air through the AIR system into the exhaust stream. The PCM supplies a ground for AIR pump relay. Battery voltage is then applied to AIR pump. The inlet filter is the only serviceable part of the pump.
• AIR Pump Relay -
  
  The AIR pump relay supplies high current to AIR pump voltage supply circuit. The PCM commands AIR relay on by supplying a ground on the control circuit of the relay. This action closes the internal contacts of the AIR relay, energizing the AIR pump.
• AIR Shut-Off Valve -
  
  The AIR shut-off valve is vacuum operated. When AIR system is enabled, engine vacuum is applied to the valve. The vacuum opens the valve and allows air from AIR pump to flow to the check valves. When inactive, the shut-off valve prevents airflow in either direction.
• AIR Vacuum Control Solenoid -
  
  The AIR vacuum control solenoid controls AIR shut-off valve. When AIR system is enabled, the PCM supplies a ground to the solenoid. This enables the solenoid, allowing engine vacuum to be applied to the AIR shut-off valve.
• Check Valves -
  
  The check valves prevent back flow of exhaust gases into AIR system. A shut-off valve that has become inoperative shows indications of exhaust gases in the outlet port, or heat-damaged hoses may indicate a check valve failure.
• Pipes/Hoses -
  
  The pipes/hoses carry air from AIR pump to the exhaust stream. The pipes/hoses can be tested for leaks using a soapy water solution. With AIR pump running, bubbles will form if a leak exists.

The PCM detects a system airflow problem by monitoring the Heated Oxygen Sensors (HO2S) and Short-Term Fuel Trim (STFT) values during normal open loop system operation. This is called a passive test. If the passive test passes, the PCM takes no further action. If the passive test fails or is inconclusive, the PCM diagnostic will proceed with an intrusive or active test. The PCM will command the AIR system on during normal closed loop operation and under normal operating conditions. This is called an active test. The active test will pass or fail based on the response from the HO2S. A lean HO2S response indicates that the AIR system is functioning normally. An increasing STFT value also indicates a normally functioning system. The AIR diagnostic consists of the combination of the passive and active tests. It requires failure of the passive and active tests on two consecutive key cycles to illuminate the MIL and store a DTC.