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 in order 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 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 0 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 system includes the following components:
| • | The AIR pump relay-- The AIR pump relay supplies high current to the AIR pump voltage supply circuit. The PCM commands the AIR relay ON by suppling a ground on the control circuit of the relay. This action closes the internal contacts of the AIR relay, energizing the AIR pump. |
| • | The AIR pump--The AIR pump supplies a filtered stream of fresh air through the AIR system into the exhaust stream. The PCM supplies a ground for the AIR pump relay. Battery voltage is then applied to the AIR pump. The filter is the only serviceable part of the pump. |
| • | The AIR vacuum control solenoid--The AIR vacuum control solenoid controls the AIR shut-off valves. When the AIR system is commanded ON, the PCM supplies a ground on the control circuit, enabling the solenoid. This action allows engine vacuum to be applied to the AIR shut-off valves. |
| • | The AIR shut-off valves--The AIR shut-off valves are named combination valves and are vacuum operated. These components incorporate a shut-off valve and a check valve assembled together in one unit and are serviced together as an assembly. When the AIR system is commanded ON, engine vacuum is applied to the valves by the AIR solenoid. The vacuum opens the AIR shut-off valves and allows air from the AIR pump to enter into the exhaust stream. |
| • | The check valve--The check valve that is designed and incorporated in the combination valve prevents back flow of exhaust gases into the AIR system. Any pipes/hoses that have shown indications of having heat damage may indicate a check valve failure. |
| • | The pipes/hoses--The pipes/hoses carry the fresh air from the pump to the exhaust stream. It includes the pipes/hoses and clamps. The pipes/hoses can be tested for leaks using a soapy water solution. With the AIR pump commanded ON, bubbles will form if a leak exists. |
| • | The filter--A plastic mesh filter located on the inlet hose of the AIR pump. This provides a clean supply of air to the AIR pump. It also helps keep debris from damaging the AIR pump. The filter can be serviced separately from the pump. |
Results of Incorrect Operation
If air flow does not enter the exhaust stream, the start up emission levels will rise. The PCM detects a system flow problem by monitoring the pre-catalyst heated oxygen sensor (HO2S) and Short Term FT. If a system flow problem is present the HO2S voltage will not indicate an expected lean condition, Short Term FT will not increase a pre-determined amount. The PCM will then set a diagnostic trouble code (DTC).
If incorrect voltage is present on the AIR vacuum control solenoid or the AIR pump relay control circuits the device will not operate. This will be detected by the PCM and a DTC will set.
The following DTCs can set if a secondary air injection fault is detected:
| • | DTC P0410-- A system air flow problem has been detected on both banks. |
| • | DTC P0412-- A vacuum solenoid control circuit problem has been detected. |
| • | DTC P0418-- An AIR pump relay control circuit problem has been detected. |
| • | DTC P1415 or P1416-- A single bank air flow problem has been detected. |
