Secondary Air Injection System Monitor

DESCRIPTION
The Secondary Air Injection (AIR) System monitor is a self-test strategy within the Powertrain Control Module (PCM) that monitors the function of the Secondary Air Injection system. The purpose of the AIR system is to control emissions during the first 20 to 120 seconds after the engine starts and for catalyst light off function. Air is forced into the exhaust manifold to oxidize the Hydrocarbons and Carbon Monoxide created by running rich at start-up.

Hardware
The Secondary Air System consists of an Electric Air Pump that provides air to the exhaust manifold, a combination Check Valve and Air Control Valve (two on some applications) that allows air to pass from the Electronic Air Pump to the exhaust system while preventing hot exhaust gases from passing back to the Electronic Air Pump. A Secondary Air Injection (AIR) bypass solenoid is used to provide a vacuum control signal to the Air Control Valve. A Solid State Relay controls the Electronic Air Pump On/Off operation. The Powertrain Control Module (PCM) provides a control circuit Electronic Air Injection (EAIR) to the Solid State Relay and a circuit Electronic Air Monitor (EAIRM) to monitor the Electronic Air Pump and the Solid State Relay to determine if the components are functioning properly and secondary air is present.

Operation
When the engine starts the PCM signals the Solid State Relay and the AIR bypass solenoid (up to delay of 10 seconds) to begin system operation. The Solid State Relay provides a start-up signal to the Electronic Air Pump. The AIR bypass solenoid applies a vacuum to the Air Control Valve causing it to open allowing air to flow into the exhaust manifolds. When the catalyst is lit-off and excess air is no longer required (up to 120 seconds), the PCM signals the SSR to stop pump operation and the AIR bypass solenoid to stop the vacuum supply to the Air Control Valve. The monitoring of the AIR system will occur once per drive cycle.

DTCs and MIL Operation
In the AIR System Monitor, when a malfunction has been present for two drive cycles, the DTC is stored in the PCM and the MIL is turned On. The MIL is turned Off after three consecutive drive cycles without the same malfunction being detected provided no other DTCs are stored that would independently turn the MIL On. The DTC will be erased from memory after 40 warm-up cycles without the malfunction being detected after the MIL is turned Off. Another method of erasing the DTC is initiating Powertrain Control Module reset.