The vehicles which use secondary air in the 2006 MY are the 2.0L PZEV Focus and the 2.3L PZEV Fusion. Both use a system with ported air. This means that airflow is delivered to each individual exhaust port. The secondary air pump is energized soon after start-up while the fuel system is in open loop. After the O2 sensors warm up, the secondary air pump may continue to be energized while the fuel system goes into closed loop fuel. The secondary air system may continue to run in closed loop fuel until the air pump is de-energized. The typical time period during which the AIR pump is energized is approximately 5 to 12 seconds.
In order to meet the 2006 MY monitoring requirements, the air pump inlet hose was routed so as to draw in airflow that has been metered by the Mass Air Flow (MAF) sensor. When the air pump is energized, the MAF sensor will show a corresponding increase in air flow. The AIR pump flow check monitors the MAF sensor signal and two air flow models during normal secondary air system operation to determine if secondary air is being delivered into the exhaust system. The air pump flow test compares the actual change in MAF during the pump on and off transitions to the expected change in air flow from the secondary air flow model. (A throttle body flow model is used to "zero out" errors in the air meter and to compensate for off idle driving conditions.) The actual air flow is divided by the expected air flow to calculate an "On flow ratio" and an "Off flow ratio". A flow ratio that is much less than 1.0 means that the air pump has no/low flow, or the inlet hose to the pump is disconnected. If secondary air system operation extends into closed loop fuel, fuel trim feedback is used to discriminate between
low pump flow and inlet hose disconnection. A low flow ratio with a lean fuel system indicates a disconnected inlet hose. A flow ratio much higher than 1.0 (and a rich fuel system indication) means that the outlet hose from the pump is disconnected.