The system uses the o2 sensor to diagnose the air injection system. After the car has warmed up, it will activate the air pump for approx 60 seconds and watches the o2 sensor voltage-as it blows air into the exhaust system it will drop the o2 sensor voltage-it needs to drop below 40mv within 60 seconds or it will trigger the light. When the air injection system is working correctly it will drop below immediately, if there is a minor restriction it may take a while: 15-30 seconds. The same is true of the o2 sensor is getting lazy, then it may take a while for the voltage to drop, it may not drop at all if the o2 sensor is really bad. Good luck.