For 1990-2009 cars

### Secondary Air Injection (AIR) System Description

(1) | Air Pump
(2) | Air Pump Solenoid
(3) | Shut-off Valve
(4) | Check valve (keeps exhaust gas from entering the air pump)
(5) | Check valve (keeps vacuum in the solenoid vacuum line)
(6) | Air pipe and hose

AIR Pump Relay Terminal Identification
Front of Vehicle | Control | B+
Pump Supply | Ignition

The secondary air injection (AIR) system reduces exhaust emissions after initial engine starts. The AIR pump operates when the start up coolant temperature is between 2°-40°C (36°-104°F) and the intake air temperature (IAT) is more than 1°C (33°F). The Powertrain Control Module (PCM) commands the AIR system ON by suppling a ground to the AIR pump relay and the AIR solenoid simultaneously. The AIR solenoid applies engine vacuum to the AIR shut-off valve, opening the valve. The AIR pump forces pressurized fresh air into the pipes/hoses and past the exhaust check valve into the exhaust manifold, accelerating catalyst operation. This fresh air causes additional combustion to take place. When the AIR system is inactive, the AIR shut-off valve and the exhaust check valve prevent airflow in either direction. The PCM runs up to two diagnostic active tests during the same key cycle using the HO2S 1 voltage parameter to verify system operation. When the PCM detects an insufficient heated oxygen sensor (HO2S) 1 response, DTC P0410 sets.

The AIR system consists of the following components:

• | The AIR pump--The AIR pump supplies pressurized, filtered air to the exhaust stream. The AIR pump is a turbine type pump which is permanently lubricated and requires no periodic maintenance.

• | The AIR solenoid--The AIR solenoid is used to apply engine vacuum to the AIR shut-off valve. The solenoid is commanded ON by the PCM. It is wired in parallel with the AIR pump to operate whenever the pump is operating. When the solenoid is energized, engine vacuum opens the AIR shut-off valve. The resistance of the AIR solenoid coil is 30 - 40 ohms.

• | The shut-off valve--During normal engine operation, the pulses in the exhaust stream create a slight vacuum at the exhaust check valve inlet. This condition can draw fresh air into the exhaust stream. The shut-off valve provides a positive seal to prevent fresh air from being drawn into the exhaust when the AIR system is inactive. The shut-off valve receives engine vacuum from the AIR solenoid to open the valve. When the valve is opened, fresh pressurized air from the AIR pump is allowed to enter the exhaust stream.

• | The exhaust check valve--The exhaust check valve is a one-way valve that allows air to flow into the exhaust system, but prevents hot exhaust gases from back-flowing into the AIR system where it could potentially damage the AIR system components. The exhaust check valve also prevents damage from occurring in the event of an exhaust backfire. When the exhaust check valve is operating properly, it will allow air to be drawn into the exhaust stream. An audible exhaust noise may be heard at the inlet of the valve.

• | The AIR pump relay--The AIR pump relay provides high current to the AIR pump motor. The PCM energizes the relay by completing the ground circuit to the relay coil. This energizes the relay and closes the internal contacts which supply voltage and high current to the AIR pump. The resistance of the AIR pump relay coil is 75 - 80 ohms.

• | Pipes and hoses--The pipes/hoses distribute the pressurized fresh air from the AIR pump to the AIR shut-off valve and the exhaust check valve. A pipe connects the exhaust check valve to the exhaust manifold. The AIR system also utilizes a hose connected to two filters to provide filtered air to the AIR pump. If these hoses are restricted or improperly secured, DTC P0410 may set.

• | The inlet filter--There are two types of inlet filters. The first type utilizes the air filter for the engine. This system draws filtered air directly from the air cleaner assembly. The second type uses a separate filter that provides filtered air exclusively for the AIR system.

• | The vacuum check valve--The vacuum check valve is a one-way valve that allows sufficient engine vacuum to be maintained in the vacuum lines to keep the AIR shut-off valve open under low engine vacuum conditions. An improperly operating vacuum check valve will allow the vacuum supply to deplete rapidly under low engine vacuum conditions. The vacuum check valve may also fail by causing a restriction in the vacuum supply to the air solenoid. A low vacuum supply to the shut-off valve will not allow the valve to open.