Oxygen Sensor: Description and Operation
OXYGEN SENSOR-PCM INPUTDESCRIPTION
The oxygen sensors (O2S) are attached to, and protrude in to, the vehicle exhaust system.
OPERATION
The sensors produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas. When a large amount of oxygen is present (caused by a lean air/fuel mixture), the sensors produces a low voltage. When there is a lesser amount present (rich air/fuel mixture) it produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensors act as a rich-lean switches.
In Closed Loop operation, the PCM monitors certain O2 sensor input(s) along with other inputs, and adjusts the injector pulse width accordingly. During Open Loop operation, the PCM ignores the O2 sensor input. The PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.
The oxygen sensors are equipped with a heating element that keeps the sensors at proper operating temperature during all operating modes. Maintaining correct sensor temperature at all times allows the system to enter into closed loop operation sooner. Also, it allows the system to remain in closed loop operation during periods of extended idle. Certain emissions packages use the Automatic Shutdown (ASD) relay to supply battery voltage to the heating elements. Other emissions packages use separate oxygen sensor relays to supply battery voltage to the heating elements.