Circuit/System Description
The secondary air injection system aids in the reduction of hydrocarbon emissions during a cold start. The electric air pump forces fresh air into the exhaust stream in order to accelerate the catalyst operation. A pressure sensor in each shutoff/check valve is used to monitor the air flow from the secondary air injection pump. The engine control module (ECM) supplies voltage to the 5-volt reference circuits and supplies a ground to the low reference circuits. The sensors provide a signal voltage to the ECM relative to the pressure changes within the secondary air injection system.
Ignition voltage is supplied to the secondary air injection pump and air injection shutoff/check valve relays. The ECM controls the relays by grounding the control circuits, which activates the relays. When the relay contacts close, voltage is supplied to the pump and the valves, which turns the pump on and opens the valves.
The diagnostic uses 3 phases to test the secondary air injection system:
- DTCs P0411, P2430 and P2435 run during Phase 1
- DTCs P2430, P2435 and P2440 run during Phase 2
- DTC P2444 runs during Phase 3
During phase 1, the secondary air injection pump and both secondary air injection shutoff and check valves are activated. Normal secondary air function occurs. Expected system pressure is 5-11kPa (0.7-1.6 psi) above BARO. Relatively high magnitude of pressure pulses are expected due to exhaust pulses. Low magnitude pressure pulses indicate a blockage or disconnect downstream of the valve.
During phase 2, only the secondary air injection pump is activated. The shutoff and check valves are closed. Pressure sensor performance and shutoff and check valve deactivation are tested. Expected system pressure is 14-22kPa (2.0-3.2 psi) above BARO.
During phase 3, neither the secondary air injection pump nor the secondary air injection shutoff and check valves are activated. Secondary air injection pump deactivation is tested. Expected system pressure equals BARO.