Oxygen Sensor: Description and Operation
UPSTREAM HEATED OXYGEN SENSORUpstream/Downstream Oxygen Sensors:
The upstream O2S sensor is located in the exhaust downpipe. It provides an input voltage to the PCM. The input tells the PCM the oxygen content of the exhaust gas. The PCM uses this information to fine tune fuel delivery to maintain the correct oxygen content at the downstream oxygen sensor. The PCM will change the air/fuel ratio until the upstream sensor inputs a voltage that the PCM has determined will make the downstream sensor output (oxygen content) correct.
The upstream oxygen sensor also provides an input to determine catalyst efficiency. Refer to Emissions, On-Board Diagnostics, Catalyst Monitor for more information.
DOWNSTREAM HEATED OXYGEN SENSOR
The downstream heated oxygen sensor is located near the outlet end of the catalytic convertor. The downstream is also used to determine the correct air fuel ratio. As the oxygen content changes at the downstream the PCM calculates how much air fuel ratio change is required. The PCM then looks at the upstream oxygen sensor voltage and changes fuel delivery until the upstream sensor voltage changes enough to correct the downstream sensor voltage (oxygen content).
The downstream oxygen sensor also provides an input to determine catalyst efficiency. Refer to Emissions Control Systems, On-Board Diagnostics, Catalyst Monitor for more information.
OXYGEN SENSOR (O2S)-HDC ENGINES- PCM INPUT
A total of two heated O2S sensors are used (left and right) on HDC engines. On the HDC engine, the left O2S sensor will monitor cylinders 1, 3, 5, 7 and 9. The right sensor will monitor cylinders 2, 4, 6, 8 and 10.
The sensors produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. 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 switch.
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.
In Closed Loop operation, the PCM monitors the O2S sensor input (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 Automatic Shutdown (ASD) relay supplies battery voltage to both oxygen sensors. The oxygen sensors are equipped with a heating elements. The heating elements reduce the time required for the sensors to reach operating temperature.
OXYGEN SENSOR (O2S)-PCM INPUT
The 8.0L V-10 engine, when equipped with a Medium Duty Emission Cycle (MDC) package, will use four heated O2S sensors. They are: Left, right, pre-catalyst and post catalyst. The left, right and post catalyst sensors will fine-tune air-fuel ratio. The pre-catalyst and post catalyst sensors will determine catalytic converter efficiency.
Left/Right Heated Oxygen Sensors:
Two of these sensors are installed into the left and right exhaust manifold downpipes. On the 8.0L V-10 MDC engine, the left O2S sensor will monitor cylinders 1, 3, 5, 7 and 9. The right sensor will monitor cylinders 2, 4, 6, 8 and 10.
The sensors produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. 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 switch.
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.
In Closed Loop operation, the PCM monitors the O2S sensor input (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 Automatic Shutdown (ASD) relay supplies battery voltage to both oxygen sensors. The oxygen sensors are equipped with a heating elements. The heating elements reduce the time required for the sensors to reach operating temperature.
PRE-CATALYST OXYGEN SENSOR
Pre-Catalyst/post Catalyst Oxygen Sensors:
The pre-catalyst O2S sensor is located in the inlet end of the catalytic converter. It provides an input voltage to the PCM. By comparing the input from the pre-catalyst O2S sensor, with the input from the post catalyst oxygen sensor, the PCM calculates catalytic convertor efficiency.
POST CATALYST OXYGEN SENSOR
The post catalyst heated oxygen sensor threads into the outlet end of the catalytic convertor. The post catalyst heated oxygen sensor input is used to detect catalytic convertor deterioration and fine tune the air fuel ratio. As the convertor deteriorates, the input from this sensor begins to match the precatalyst sensor input except for a slight time delay. By comparing the inputs from both of these sensors, the PCM calculates catalytic convertor efficiency.
When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic trouble code and illuminates the Malfunction Indicator Lamp (MIL). For more information, refer to Emission Control Systems.