PGM-FI System Description - A/F Sensor/HO2S Feedback Air/Fuel Ratio Control

Air fuel ratio control is part of fuel injection control and comprises the steps of:

	Calculating basic injection amount from intake air flow amount and engine speed
	Calculating air fuel ratio correction value from the oxygen density in the exhaust gas and reflecting the calculated values to the injection amount

Air fuel ratio control stops feedback under the following conditions in order to maintain operational performance and catalytic protection.

	When starting the engine or during fuel increase after the engine is started
	While the engine coolant is cold
	During fuel increase under high load
	During fuel increase at high engine speed
	During fuel cut-off at deceleration

Air Fuel Ratio (A/F) Sensor (Sensor 1)

Air fuel ratio control performs fuel injection control based on the oxygen density detected in exhaust gas in order to bring the intake mixture in the vicinity of a target air fuel ratio.
This high-precision air fuel ratio control is realized by detecting a correction value with an air fuel ratio (A/F) sensor (Sensor 1) and then applying further correction with a secondary heated oxygen sensor (secondary HO2S) (Sensor 2).
The powertrain control module (PCM) supplies a current to the A/F sensor (Sensor 1), and monitors the current value which varies with the oxygen density in the measuring chamber of the sensor.
The current value is proportional to the air fuel ratio, therefore the PCM can calculate the air fuel ratio from the value of the current.

Secondary HO2S (Sensor 2)

The secondary heated oxygen sensor (secondary HO2S) (Sensor 2) detects the oxygen density in the exhaust gas passing through the catalyst and outputs it to the powertrain control module (PCM) to enable the high-precision air fuel ratio control, which cannot be realized only with an A/F sensor (Sensor 1).
A ceramic heater is equipped inside the element in order to shorten sensor reaction time and to enable output that is constantly stable.