Secondary Air Injection System: Notes

The Secondary Air Injection (AIR) system is designed to reduce exhaust emissions during cold or warm engine starts. The AIR pump is timed to run approximately one minute when the engine is first started. The Powertrain Control Module (PCM) commands the AIR system ON by supplying a ground on the AIR pump relay and the AIR solenoid control circuits. This action energizes the AIR pump and AIR solenoid. The PCM uses an internal switch called a driver to supply a ground to these devices. The PCM also monitors the voltages on these circuits to perform its diagnostic tests. The action of the PCM commanding the AIR solenoid ON, allows engine vacuum to be applied to the AIR shut-off valves, opening the valves. The action of the PCM commanding the AIR relay ON, energizes the AIR pump. The AIR pump then forces fresh air past the shut-off valves, through the pipes/hoses and then into the exhaust system to accelerate catalyst operation. When The AIR system is inactive the shut-off valves prevents airflow in either direction.

The PCM will perform a passive test while the AIR system is performing normally. During the test the PCM monitors the Heated Oxygen Sensors (HO2S) voltages, expecting a drop below 100 mV. The PCM expects the Short Term Fuel Trim (FT) to increase at the same time. If the test fails or is inconclusive the PCM diagnostic will proceed with an intrusive or active tests. The PCM will command the AIR system ON during normal Closed Loop operation and under normal operating conditions. The PCM will run up to 3 diagnostic active tests using the HO2S voltage parameter and Short Term FT parameter to diagnose the system operation. The AIR diagnostic consists of the combination of the passive and the active tests, two consecutive trips are required to illuminate the MIL and store a DTC. A trip is the completion of one AIR test which occurs only once per key cycle and warm up cycle. When the PCM detects an insufficient HO2S response on both engine banks Diagnostic Trouble Code (DTC) P0410 sets. If the PCM detects only one engine bank did not respond DTC P1415 or P1416 sets. As the PCM monitors the control circuits of the AIR pump relay and AIR solenoid it expects to see a high voltage when they are OFF. When commanded ON the PCM expects to see a low voltage near zero volts, if the PCM detects a voltage other than what is expected on the AIR solenoid control circuit DTC P0412 sets. If the PCM detects an improper voltage level on the AIR pump relay control circuit DTC P0418 sets.

The AIR system includes the following components: