Air Injection: Description and Operation

Secondary Air Injection Diagram:

CONSTRUCTION
The Electric Secondary Air (AIR) System consists of an Electric Air Pump (EAP), a combination Check and Air Diverter (AIRD) valve(s), an AIR Bypass solenoid, A Solid State Relay (SSR), Powertrain Control Module (PCM), connecting wires and vacuum hoses.

PURPOSE
The Electric Secondary AIR system controls emissions during the first 20-120 seconds of engine operation. the AIR system forces air downstream into the exhaust manifolds to oxidize the hydrocarbons and carbon monoxide created by running rich at start-up.

OPERATION

Cold Engine Operation
- When the engine is started, PCM signals the SSR and the AIR By-Pass solenoid, after a few seconds delay, to begin system operation.

- The Solid State Relay provides the start up signal and switches the high current required to operate the EAP. The EAP provides air until the catalyst is lit-off and can oxidize and reduce emissions.

- The AIR Bypass solenoid applies a vacuum to the AIRD valve(s) causing it / them to open allowing air to flow into the exhaust manifold through the inlet.

Warm Engine Operation
Once the Catalyst is lit-off, the PCM signals the SSR to stop pump operation and the AIR Bypass solenoid to stop the vacuum supply to the AIR Diverter valve(s).

Secondary Air Injection System Monitor
Is an on-board strategy designed to monitor the proper function of the Secondary AIR system.

System Functional Check
Is a designed to test the ability of the AIR system to inject air into the exhaust. The functional check may be done in two parts; at start-up when the Air Pump is normally commanded on, or during a hot idle if the start-up was not able to be performed. The flow test relies upon the Heated Oxygen Sensor (HO2S) to detect the presence of additional air in the exhaust when introduced by the Secondary Air Injection system.

The System Consists of Two Monitor Circuits:

Primary Circuit
An AIR circuit to diagnose the problems with the primary circuit side of the SSR. The AIR circuit is normally held high through the Secondary AIR Bypass solenoid and SSR when the output driver is off. Therefore a low circuit indicates a driver is always on and a high circuit indicates an open in the PCM. The Diagnostic Trouble Code (DTC) associated with this test is DTC PO412.

Secondary Circuit
An AIR Monitor circuit to diagnose problems with the secondary circuit side of the SSR. The AIR Monitor circuit is held low by the resistance path through the Air Pump when the pump is off. If the AIR Monitor circuit is high, there is either an open circuit to the PCM from the pump or there is power supplied to the Air Pump. If the AIR Monitor is low when the pump is commanded on, there is either an open circuit from the SSR or the SSR has failed to supply power to the pump. DTC's associated with this test are DTCs P1413 and P1414.