The two AIR pumps used on this vehicle lower tail pipe
emissions during start-up. The AIR system consists of the following items:
| • | AIR relays, fuses, and related wiring |
The PCM uses the AIR relays to control the AIR pumps. The PCM also controls
the AIR vacuum solenoid that supplies vacuum to the AIR check valves. With
the AIR system inactive, the AIR check valves prevent air flow in either direction.
With the AIR system active, the PCM applies ground to one of the AIR relays,
and the vacuum solenoid. After a few seconds, the PCM applies ground to the
other AIR relay. Fresh air flows from the pumps, through the system hoses,
pass the check 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 AIR system for the following conditions:
| • | AIR system (overall system including both banks, and results in
DTC P0410) |
| • | AIR system bank 1 (DTC P1415) |
| • | AIR system bank 2 (DTC P1416) |
| • | AIR relays (DTC P0418, and DTC P0419) |
| • | AIR vacuum control solenoid (DTC P0412) |
The PCM runs two tests to diagnose the AIR system, Passive and Active.
Both tests contain two parts, and involve a response from the fuel control
HO2 sensors (HO2S bank 1 sensor 1 and HO2S bank 2 sensor 2)
as follows:
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 freezes the fuel trim
system, then 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 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 HO2 sensors with the AIR system turned OFF. With the AIR system turned
OFF, the PCM unfreezes the fuel trim system, then 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 PART 1
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 freezes the fuel
trim system, then 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 starts part 2 of the active test.
ACTIVE TEST PART 2
The PCM performs part 2 of the active test to watch the response of
the HO2 sensors with the AIR system turned OFF. During warmed-up, closed-loop
fuel control, the PCM turns OFF the AIR system. The PCM unfreezes the fuel
trim system, then 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.
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. If the PCM determines that the HO2S voltages did not respond
as expected during the tests, DTC P0410 will set. If the PCM determines
that the HO2S voltage for a specific bank did not respond as expected, DTC P1415
or DTC P1416 will set, depending upon the bank.
