Description And Operation: 2.4L
The engine is equipped with two heated oxygen sensors:
- The upstream oxygen sensor (1) is referred to as the 1/1 sensor.
- The downstream oxygen sensor (2) is referred to as the 1/2 sensor.
The 1/1 upstream wide-band (6-wire) oxygen (O2) sensor consists of a heating element, a measurement chamber and a detection chamber with oxygen pumping capabilities. The oxygen pumping function is the ability to pump oxygen into or out of the measurement chamber depending on the level of oxygen in the measurement chamber. The O2 Sensor Pump Cell Current voltage will switch from approximately 0.45 volts above and below the fixed O2 Sensor Return voltage, allowing current to flow in either direction through the pump. This correlates with the pumping of oxygen into and out of the measurement chamber. When the exhaust stream has a lean air/fuel ratio (high oxygen content) the Pump Cell Current voltage will move toward +0.45 volts pumping oxygen out of the measurement chamber. When the exhaust stream has a rich air/fuel ratio (relatively low oxygen content) the Pump Cell Current voltage will move toward -0.45 volts pumping oxygen into the measurement chamber (this happens very quickly and the voltage reading may appear as a steady 0.45 volts). This function provides the wide-band sensing capabilities and is critical for proper upstream oxygen measurement.
The 1/2 downstream (4-wire) oxygen (O2) sensor is equipped with a galvanic battery that typically generates a voltage signal between 0.0 volts and 1.0 volts. The 4-wire O2 Sensor also includes a heating element that keeps the sensor at proper operating temperature during all operating modes. A bias voltage in the Powertrain Control Module (PCM) shifts the signal voltage to fluctuate between 2.5 volts and 3.5 volts, 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 sensor produces a low voltage. When there is a lesser amount of oxygen present (caused by a rich air/fuel mixture) it produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch.
In Open Loop operation the PCM ignores input from both O2 sensors. In Closed Loop operation the PCM monitors the O2 sensor's input (along with other inputs) and adjusts the injector pulse width accordingly based on preprogrammed (fixed) values and inputs from other sensors. 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. The PCM also compares upstream and downstream O2 Sensor inputs to calculate the catalytic convertor oxygen storage capacity and converter efficiency. If the catalytic converter is working properly, the oxygen content of the exhaust gases at the converter outlet (downstream) fluctuate significantly less than the converter inlet (upstream). The PCM compares the switching rates of both downstream and upstream O2 Sensors under specific operating conditions to determine if the catalyst is functioning properly.