The injection system is composed of the air pump, exhaust manifold, inlet check valve, and vacuum control switch, besides, the switch has an electrical circuit and there are vacuum hoses. This system sends fresh air into the exhaust on cold starts, thus oxygen and exhaust gases are fed. This ensures complete hydrocarbon combustion. After approximately one minute, the system shuts itself down.
The error code P0491 OBDII is set when there is a failure in this system, this usually happens because the secondary airflow is too low in bank 1.