Secondary Air Injection (AIR) System Description
The Secondary Air Injection (AIR) System reduces exhaust emissions following
initial engine start up. This occurs when the engine Start-up coolant temperature
is between 3-50°C (37-122°F) and the intake air temperature (IAT)
is more than 1°C (32°F). The AIR pump will operate until Closed Loop operation
is achieved.
The powertrain control module (PCM) activates the AIR system by suppling a ground
to the AIR pump relay and AIR solenoid relay simultaneously. This action closes the
internal contacts of the AIR pump relay, energizing the AIR pump and also closes the
internal contacts of the AIR solenoid relay, energizing the AIR solenoid, opening
the shut-off valve. The AIR pump forces pressurized fresh air into the pipes/hoses
and past the check valve into the exhaust manifold, accelerating catalyst operation.
When the AIR system is inactive, the AIR shut-off valve prevents airflow in either
direction.
The AIR system includes the following components:
| | The AIR pump supplies pressurized,
filtered air to the exhaust stream. The AIR pump is a turbine type pump which is permanently
lubricated ad requires no periodic maintenance. The AIR pump for the 4.2 liter
engine will draw a steady 35-40 amps under normal operation. The AIR
pump has an internal circuit breaker to protect the pump from overheating. The circuit
breaker is an integral part of the AIR pump. |
| | The AIR shut-off valve has an electronic
solenoid mounted on the valve. The resistance of the solenoid is 4-7 ohms
and the current draw is 2-3.5 amps. The solenoid opens the shut-off valve
when battery voltage is applied to the valve. Once opened, pressurized air from the
AIR pump flows past the check valve and is directed into the bank 1 exhaust
manifold through an outlet pipe. The shut-off valve prevents fresh air from being
drawn into the exhaust manifold by providing a positive seal when the AIR system is
inactive. The solenoid, valve, and outlet pipe are serviced as an assembly. |
| | Important: An audible exhaust noise may be heard at
the inlet of the shut-off valve, when the shut-off valve is opened and the AIR pump
outlet hose is removed from the shut-off valve.
|
| | The AIR pump relay supplies high current
and battery voltage to the AIR pump. The resistance of the AIR pump relay coil is
55- 68 ohms. |
| | The AIR solenoid relay supplies high
current and battery voltage to the AIR solenoid that is an integral part of the shut-off
valve. The PCM commands the AIR solenoid relay ON by suppling a ground on the control
circuit of the relay. The resistance of the AIR pump relay coil is 80-90 ohms. |
| | The pipes/hoses carry the air from the
AIR pump past the AIR shut-off valve, and into the exhaust manifold. A pipe connects
the shut-off valve to the exhaust manifold. The AIR System also utilizes a hose to
carry the filtered air to the inlet of the AIR pump. |
| | The filter utilizes the air filter for the
engine. This system draws filtered air directly from the air cleaner assembly. |
Results of Incorrect Operation
The PCM can detect an AIR System airflow fault by monitoring the heated oxygen
sensor (HO2S) bank 1 sensor 1 during normal engine operation. This is
an active test. The PCM will command the AIR system ON during Closed Loop operation
to perform this test. The active test will pass or fail based on the response from
the HO2S 1. The active test consists of three tests run at 3-second intervals.
A decreasing HO2S voltage parameter response indicates that the secondary AIR system
is functioning properly. If the PCM does not detect a decreasing response from the
HO2S 1, DTC P0410 will set.
