Upstream Oxygen Sensor
Upstream oxygen sensor is a heated oxygen sensor mounted on the exhaust manifold. See Fig 1 and Fig 2 . Heater is used on upstream oxygen sensor so sensor reaches operating temperature quicker and maintains sensor at operating temperature during all operating modes. Heater on upstream oxygen sensor receives voltage from Auto Shutdown (ASD) relay. For operation of ASD relay, see RELAYS under MISCELLANEOUS CONTROLS.
The input from the upstream heated oxygen sensor tells the Powertrain Control Module (PCM) the oxygen content of the exhaust gas. Based on this input, the PCM fine tunes the air-fuel ratio by adjusting injector pulse width. The sensor input switches from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold (this is offset by 2.5 voltage on NGC vehicles). When a large amount of oxygen is present (caused by a lean air-fuel mixture), the sensor produces voltage as low as 0.1 volt. When there is a lesser amount of oxygen present (rich air-fuel mixture) the sensor produces a voltage as high as 1.0 volt. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch. The heating element in the sensor provides heat to the sensor ceramic element. Heating the sensor 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. In Closed Loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other inputs. In Open Loop, the PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.
Upstream oxygen sensor produces a small electrical voltage input signal to PCM depending on amount of oxygen content in the exhaust gas. Upstream oxygen sensor produces a low voltage when a large amount of oxygen exists in exhaust gas (lean condition) and a higher voltage when a lesser amount of oxygen exists in exhaust gas (rich condition). The heating element in the sensor provides heat to the sensor ceramic element. Heating the sensor allows the system to enter closed-loop operation sooner. It also allows the system to remain in closed-loop operation during periods of extended idle. In closed-loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other inputs. In open-loop, the PCM adjusts injector pulse width based on preprogrammed (fixed) values and inputs from other sensors.