RAM 1500 Van V8-5.2L CNG VIN T (1999)
Oxygen Sensor: Description and Operation
OXYGEN SENSOR (O2S) - PCM INPUT
Two heated O2S sensors are used. 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 the upstream and downstream heated oxygen sensors. The oxygen sensors
are equipped with a heating element The heating elements reduce the time required for the sensors to reach operating temperature.
UPSTREAM HEATED OXYGEN SENSOR
Heated Oxygen Sensors
The upstream O2S sensor is located in the inlet end of the catalytic converter. 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 the air/fuel ratio by adjusting injector pulse width.
DOWNSTREAM HEATED OXYGEN SENSOR
The downstream heated oxygen sensor threads into the outlet end of the catalytic convertor. The downstream heated oxygen sensor input is used to
detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream sensor begins to match the upstream sensor
input except for a slight time delay. By comparing the downstream heated oxygen sensor input to the input from the upstream sensor, 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.
