Purpose
The secondary air injection (AIR) system aids in the reduction of hydrocarbon
emissions. During Open-Loop fuel control, air is injected into the exhaust
stream for a specified amount of time. Heat generated from post-combustion
oxidation helps the catalytic converter reach operating temperature sooner,
referred to as converter light off. The following conditions determine
pump operation:
| • | Start-up ECT and IAT must be more than 4.4°C (40°F) but
less than 30°C (86°F). |
| • | Start-up BARO must be more than 75 GPA. |
| • | The start-up conditions will operate for 70 seconds or until the
vehicle reaches Closed Loop. |
Secondary Air Injection Bleed-off Valve
A remotely mounted bleed-off valve releases vacuum in the AIR system.
The valve is similar in construction and operation to the evaporative purge
control solenoid. As the mass flow of the exhaust gases pass the injection
piping, a venturi vacuum effect occurs. The vacuum is strong enough to
hold the internal shut-off valve closed when the powertrain control module
(PCM) commands the secondary air ON. An inline check valve prevents air
from escaping through the bleed valve when the pump is commanded ON.
Secondary Air Injection Check Valves
Check valves remain the same as those used in earlier AIR systems. The
valves are made of heat and corrosion resistant material. Located in the AIR
piping to each bank, check valves prevent exhaust backflow when AIR is
commanded OFF or an exhaust backfire occurs.
Secondary Air Injection Hoses, Clamps, and Pipes
AIR hoses are made of heat resistant, non-reinforced rubber. Clamps,
designed for high temperature conditions, connect the hoses to the pump and
check valve/pipe assemblies of each cylinder bank. The air injection pipes,
connected to the exhaust manifolds, are high temperature, corrosion resistant
stainless steel.
Operation
The secondary air injection reaction (AIR) system is controlled by the
PCM. After PCM replacement the air pump is not allowed to run until the mileage
is more than 10 miles. At start-up, the PCM energizes the AIR system relay.
Battery voltage is supplied to the AIR pump, and bleed-off valve until
the system enters Closed Loop or for a maximum time of 70 seconds, which
ever occurs first. Air from a remotely mounted filter is drawn into the
pump by centrifugal action, pressurized, and pumped through check valves
into the exhaust stream. Without the bleed-off valve, a vacuum would build
in the AIR hoses due to the venturi effect created as the exhaust gases
flow past the injection piping. The vacuum is strong enough to hold the
internal shut-off valve closed. To prevent this situation, the bleed-off
valve vents the vacuum to atmosphere. An inline check valve prevents air
from escaping through the bleed-off valve during injection. Check valves
in the AIR piping to each cylinder bank prevent exhaust backflow when AIR
is commanded OFF or an exhaust backfire occurs.
The PCM monitors the AIR system in two stages, Passive and Active. The
PCM initiates a two part Passive Test once each ignition cycle. Part one
monitors the HO2S response when the PCM commands the air pump ON. If the
HO2S remains proportionally lean, low HO2S signal, Passive Test 1 passes
and Passive Test 2 is initiated. The Passive Test 2 monitors the transition
from Open Loop to Closed Loop fueling. When air injection to the exhaust
is commanded OFF, the PCM monitors the HO2S response. If the HO2S signal
switches from a lean to rich condition for a specific amount of time, part
two passes. If part one and part two pass, further monitoring of the AIR
system is discontinued. If any portion of the Passive Test fails, the PCM
initiates the Active Test. To run the Active Test, the AIR pump is commanded
ON during warmed-up, Closed Loop operation. The PCM monitors the HO2S and
long and short term fuel trim value response to air injection. If the HO2S
signal remains proportionally lean for a specific amount of time, low
HO2S signal, or the short term fuel trim values increase, the Active Test
passes. If both HO2S1 signal and short term fuel trim values do not respond
to air injection, the Active Test fails. If the PCM detects a consecutive
number of Active Test failures, DTC P0410 will set. If a successful
test occurs during the Active Test stage, a pass indication results and
the test will not run until the next ignition cycle. The following conditions
set the AIR system fault:
| • | Active VSS, TP Sensor, EVAP System, HO2S Sensor, Misfire, IAT
Sensor, MAP Sensor, IAC, Fuel Trim, Fuel Injector Circuit, EGR Pintle, ECT
Sensor, CKP Sensor, or MAF Sensor DTCs are not set. |
| • | Engine run time is more than 1 second. |
| • | System voltage is more than 11 volts. |
Passive Tests
| • | ECT sensor signal indicates temperatures more than 4.4°C (40°F)
but less than 30°C (86°F). |
| • | Engine load is less than 80 percent. |
| • | MAF is less than 35 gm/s. |
| • | HO2S1 signal voltage must remain less than 350 mv for more than
60 seconds to pass. |
| • | HO2S1 signal voltage must remain more than 600 mv for more than
45.5 seconds to fail. |
Active Tests
| • | ECT sensor signal indicates temperatures more than 75°C (167°)
but less than 110°C (230°F). |
| • | MAF is less than 15 gm/s. |
| • | Engine load is less than 40 percent. |
Operation Summary
| • | If the Passive tests pass the Active Test will not run and no
DTCs will set. |
| • | If either of the Passive tests are inconclusive the Active Test
will run and must fail 3 times for a DTC to set. |
| • | If either of the Passive tests fail then the Active Test will
run and must fail 2 times for a DTC to set. |
| • | If either of the Passive Tests conditions are exceeded, Passive
Tests By Pass, the Active Test will run and must fail 3 times for
a DTC to set. |
Results of Incorrect AIR System Operation
If during Open Loop fuel control, air injection is not present in the
exhaust stream, high first and second hydrocarbon emissions result.
Continuous air injection to the exhaust stream will result in the following
conditions:
| • | Open Loop fuel control will be in effect. |
| • | Backfiring in the exhaust/catalyst system may occur. |
| • | Catalyst damage may occur. |
No air injection to the exhaust stream will result in the following
conditions:
| • | High Hydrocarbon and Carbon Monoxide emissions will occur during
Open Loop fuel control. |
Diagnosis
The PCM monitors the Secondary Air Injection Reaction (AIR) System.
A system malfunction will set DTC P0410.
