Circuit Description

An AIR pump is used to lower tailpipe emissions on start-up. PCM grounds the AIR pump relay control circuit, which energizes AIR pump. PCM also grounds the AIR combination valve vacuum control solenoid circuit, which energizes the AIR vacuum control solenoid. 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, AIR pump forces fresh air into exhaust stream in order to accelerate catalyst operation. The AIR combination valves replace the conventional check valves. When AIR system is inactive the shut-off valves prevent air flow in either direction. DTC will set when there is a problem with AIR vacuum control solenoid circuit.