For 1990-2009 cars

### Purpose

The secondary air injection system (AIR) 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 greater than 4.4°C (39.92°F) but less than 30°C (86°F).

• | Start up BARO must be greater than 75 GPA.

• | The start up conditions will operate for 70 Seconds or till 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 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 greater 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, witch 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. Conditions for setting the AIR system fault:

• | No 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 set.

• | Engine run time more than 1 seconds.

• | System voltage is more than 11 volts.

• | Passive Tests

- | ECT sensor signal indicates temperatures greater than 4.4°C (39.92°F) but less than 30°C (86°F).

- | Engine load less than 80 percent .

- | MAF less than 35 gm/s

- | HO2S1 signal voltage must remain less than 350 mv for greater than 60 seconds to pass.

- | HO2S1 signal voltage must remain greater than 600 mv for greater than 45.5 seconds to fail.

• | Active Test

- | ECT sensor signal indicates temperatures greater than 75°C (167°) but less than 110°C (230°F)

- | MAF less than 15 gm/s

- | HO2S1 signal voltage

- | Engine load 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:

• | DTC P0410 will set.

• | 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:

• | DTC P0410 will set.

• | High hydrocarbon and carbon monoxide emissions will occur during open loop fuel control.

### Diagnosis

The powertrain control module (PCM) monitors the secondary air injection reaction (AIR) system. A system malfunction will set DTC P0410.