Upstream Oxygen Sensor

The input from upstream heated oxygen sensor tells PCM oxygen content of exhaust gas. Based on this input, PCM fine tunes air-fuel ratio by adjusting injector pulse width.

The sensor input switches from 0-1 volt, depending upon oxygen content of exhaust gas in exhaust manifold. When a large amount of oxygen is present (caused by a lean air-fuel mixture), sensor produces voltage as low as .1 volt. When there is a lesser amount of oxygen present (rich air/fuel mixture) sensor produces a voltage as high as 1.0 volt. By monitoring oxygen content and converting it to electrical voltage, sensor acts as a rich-lean switch.

The heating element in sensor provides heat to sensor ceramic element. Heating sensor allows system to enter into closed loop operation sooner. Also, it allows system to remain in closed loop operation during periods of extended idle.

In Closed Loop, PCM adjusts injector pulse width based on upstream heated oxygen sensor input along with other inputs. In Open Loop, PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.