This vehicle has two Secondary AIR systems: a dual pump
system (early production), and a single pump system (later production). The
secondary AIR system is used to lowers tail pipe emissions during start-up.
The AIR systems consists of the following items:
| • | The vacuum control solenoid valve |
| • | The system hoses and pipes |
| • | The AIR relay(s), fuses, and related wiring |
The PCM uses the AIR relay(s) to control the AIR pump(s). The PCM also
controls the AIR vacuum control solenoid valve that supplies vacuum to the
AIR shutoff valves. With the AIR system inactive, the AIR shutoff valves
prevent air flow in either direction. With the AIR system active, the
PCM applies ground to the AIR relay(s), and the vacuum control solenoid
valve. Fresh air flows from the pump, through the system hoses, pass
the shutoff valves, and into the exhaust stream. The air helps the catalyst
to quickly get to a working temperature; thus lowering the tail pipe
emissions on a start-up. The PCM tests the following AIR system components:
| • | The overall AIR system, including both banks -- any problems
detected here will result in DTC P0410. |
| • | The AIR system bank 1 (DTC P1415) |
| • | AIR system bank 2 (DTC P1416) |
| • | AIR relay(s) (DTC P0418 and if equipped with two AIR pumps DTC
P0419) |
| • | AIR vacuum control solenoid valve (DTC P412) |
The PCM runs two tests to diagnose the AIR system: Passive, and Active.
Both tests involve a response from the fuel control HO2 sensors (HO2S bank 1
sensor 1 and HO2S bank 2 sensor 2). The Passive
test consists of two parts. If both passive tests pass, the PCM takes no
further action. If either part of the passive test fails, or is inconclusive,
the PCM initiates the Active tests.
PASSIVE TEST PART 1
The PCM performs the passive test part 1 during the normal operation
of the AIR system (start-up). The PCM initiates this test only once per key
cycle. When the PCM enables the AIR system, the PCM manipulates the fuel trim
system, then checks the voltage from the HO2S. If the PCM detects HO2S voltages
below the calibrated value for the calibrated amount of time, the PCM starts
part 2 of the passive test.
PASSIVE TEST PART 2
The PCM performs part 2 of the passive test to watch the response of
the HO2S with the AIR system turned OFF. With the AIR system turned OFF, the
PCM watches the HO2S voltages. If the PCM detects HO2S voltages that switch
from lean to rich value for a specific amount of time, the PCM passes the
AIR system.
ACTIVE TEST
The PCM performs part 1 of the active test during warmed-up, Closed-Loop
fuel control. When the PCM turns ON the AIR system, the PCM checks the voltage
from the HO2 sensors. If the PCM detects HO2S voltages below the calibrated
value for the calibrated amount of time, the PCM then commands the AIR system
OFF. If the PCM detects HO2S voltages that switch from lean to rich value
for a specific amount of time, the PCM passes the AIR system.
