GM Service Manual Online
For 1990-2009 cars only

Secondary Air Injection System Description

The secondary air injection (AIR) pump system is designed to lower exhaust emission levels on engine start-up.

The powertrain control module (PCM) commands the AIR pump relay ON, by supplying a ground on the air pump relay control circuit. This action energizes the AIR pump forcing fresh air, oxygen, into the exhaust stream. The PCM also commands the secondary air injection (AIR) solenoid ON, by supplying a ground on the air solenoid control circuit. With the AIR solenoid activated engine vacuum is applied to the AIR shut-off valve. Fresh air from the AIR pump then enters into the exhaust stream, accelerating catalyst operation, reducing exhaust emission levels. When the AIR system is inactive, the AIR shut-off valve and the exhaust check valves prevent airflow in either direction.

The secondary air injection (AIR) system includes the following components:

    â€¢ The AIR pump relay-- The AIR pump relay supplies high current to the AIR pump. The PCM commands the AIR pump relay ON by suppling a ground on the control circuit of the relay. This action closes the internal contacts of the AIR pump relay, energizing the AIR pump.
    â€¢ The AIR pump--The AIR pump supplies fresh air to the exhaust stream. The inlet hose and filter is the only serviceable part of the pump.
    â€¢ The AIR injection solenoid--The AIR injection solenoid controls the AIR shut-off valve. When the AIR system is enabled, the PCM supplies a ground on the control circuit of the air solenoid. This enables the air solenoid, allowing engine vacuum to be applied to the AIR shut-off valve.
    â€¢ The AIR shut-off valve--The AIR shut-off valve is vacuum operated. When the AIR system is enabled, engine vacuum is applied to the valve. The vacuum opens the shut-off valve allowing fresh air from the AIR pump to flow to the exhaust check valves. When inactive the shut-off valve prevents airflow in either direction.
    â€¢ The exhaust check valves--The exhaust check valves prevent back flow of exhaust gases into the AIR system. A shut-off valve that has become inoperative, showing indications of exhaust gases in the outlet port, or heat damaged hoses may indicate an exhaust check valve failure.
    â€¢ The pipes/hoses--The pipes/hoses carry the air from the AIR pump to the exhaust stream. The pipes/hoses can be tested for leaks using a soapy water solution, with the AIR pump running, bubbles will form if a leak exists.

Results of Incorrect Operation

The PCM detects a system airflow problem by monitoring the heated oxygen senors (HO2S) and Short Term Fuel Trim (FT) values during normal Open Loop system operation. This is a passive test. If the passive test indicates a pass, 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 an active test. The active test will pass or fail based on the response from the HO2S. A drop in the HO2S response indicates that the AIR system is functioning normally. An increasing Short Term FT value also indicates a normally functioning system. The AIR diagnostic consists of the combination of the passive and active test. It requires failure of the passive and active tests on two consecutive key cycles to illuminate the malfunction indicator lamp (MIL) and store a DTC. If the PCM detects that the HO2S and Short Term FT did not respond as expected on both of the engine banks DTC P0410 sets. If the PCM detects that the HO2S and Short Term FT did not respond as expected on only one of the engine banks DTC P0491 for bank 1 or P0492 for bank 2 sets.

If incorrect voltage is present on the AIR solenoid or the AIR pump relay control circuits the device will not operate. This condition can be detected by the PCM, DTC P0412 for the AIR solenoid or P0418 for the AIR pump relay sets.

The following DTCs can set if a secondary air injection fault is detected:

    â€¢ P0410-- A system flow problem has been detected.
    â€¢ P0412-- A secondary AIR injection solenoid control circuit problem has been detected.
    â€¢ P0418-- A secondary AIR pump relay control circuit problem has been detected.
    â€¢ P0491--A Bank 1 airflow problem has been detected.
    â€¢ P0492--A Bank 2 airflow problem has been detected.