Circuit Description

A Secondary Air Injection (AIR) pump is used lower tailpipe emissions on start-up. PCM grounds the AIR pump relay control circuit, which energizes the AIR pump. PCM also grounds the AIR combination valve vacuum control circuit, which energizes the AIR vacuum solenoid valve. Vacuum is then applied to both AIR combination valve diaphragms which open the shut-off valves. PCM enables both circuits simultaneously when AIR system operation is desired. When AIR system is active, the AIR pump forces fresh air into exhaust stream in order to accelerate catalyst operation. The AIR solenoid valves replace the conventional check valves. When AIR system is inactive, the shut-off valves prevent air flow in either direction. DTC will set if an air flow problem is detected.

DTC will set when the pre-catalyst HO2S voltage remains greater than 300 mV (passive) or 150 mV (active) for a calibrated period of time and the Short Term FT does not increase a calibrated amount during the test, and both conditions exist for 3 consecutive tests.