Secondary Air Injection System Description: Notes

The Secondary Air Injection System aids in the reduction of hydrocarbon exhaust emissions during a cold start. This occurs when the start-up engine coolant temperature (ECT) is between -12 and +38°C (10-100°F), the intake air temperature (IAT) is greater than -12°C (+10°F) and it has been more than 10 s since the last start. The secondary air injection pump operates 5-60 s after start-up.

The engine control module (ECM) activates the secondary air injection system by simultaneously completing the ground paths for the secondary air injection pump and the secondary air injection shutoff and check (solenoid) valve relay. This action closes the relays' internal contacts. The pump and shutoff and check valve are in turn energized. The pump turns ON and the valve opens.

The secondary air injection pump sends pressurized fresh air into the pipes/hoses, through the open shutoff and check valve and into the exhaust manifold. The extra air accelerates the catalyst operation, helping it to reach operating temperature faster. The secondary air injection pump remains ON for a short period of time after the shutoff and check valve is commanded OFF. When the pump is commanded OFF it will not run or be activated until the next vehicle cold start. When the secondary air injection system is inactive, the shutoff and check valve is closed to prevent air/exhaust flow in either direction.

The ECM monitors the secondary air injection system pressure by tracking the voltage signal which is provided by pressure sensor in the exhaust.

The ECM utilizes a 3 phase diagnostic routine to test the secondary air injection system:

During phase 1, DTCs P0411 and P2430 run and both the secondary air injection pump and the shutoff and check valve is activated. Normal secondary air function occurs. Expected system pressure is 6-14 kPa (0.9-2.0 psi) above BARO.

During phase 2, DTCs P2430 and P2440 run and only the secondary air injection pump is activated. The shutoff and check valve is closed. Pressure sensor performance and shutoff and check valve deactivation are tested. Expected system pressure is 22-30 kPa (3.2-4.4 psi) above BARO.

During phase 3, DTC P2444 runs and neither the secondary air injection pump nor the shutoff and check valve is activated. Secondary air injection pump deactivation is tested. Expected system pressure equals BARO.

The secondary air injection system includes the following components:

• The secondary air injection pump-The electric secondary air injection pump supplies pressurized, filtered air to the secondary air injection shutoff and check valve. The secondary air injection pump is a turbine type pump that is permanently lubricated and requires no periodic maintenance.
• The secondary air injection shutoff and check valve assembly-The shutoff and check valve assembly have direct current (DC) motor operated valves. When the valve motor is energized by the secondary air injection shutoff and check (solenoid) valve relay, the valve opens, pressurized air from the secondary air injection pump flows through the valve and is directed into the exhaust manifold.
  NOTE: The secondary air injection shutoff and check valve and the pressure sensor are serviced as an assembly.
• The secondary air injection pressure sensor-The pressure sensor is integral to the secondary air injection shutoff and check valve assembly. The sensor is a 3-wire sensor that measures the secondary air injection system pressure at the inlet of the shutoff and check valve assembly.
• The secondary air injection pump relay-The relay supplies high current and battery voltage to the secondary air injection pump. The ECM commands the relay ON by supplying a ground to the relay control circuit.
• The secondary air injection shutoff and check (solenoid) valve relay-The relay supplies high current and battery voltage to the secondary air injection shutoff and check valve. The ECM commands the relay ON by supplying a ground to the relay control circuit.
• The pipes and hoses-The secondary air injection pump inlet hose carries filtered air from the engine intake air cleaner to the secondary air injection pump inlet. The secondary air injection pump pipe carries the air from the pump outlet to the shutoff and check valve which in turn feeds the exhaust manifold.