Grand Cherokee 2WD V8-5.2L VIN Y (1998)
Oxygen Sensor: Description and Operation
OXYGEN SENSOR (02S)-PCM IN PUT
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.
In Closed Loop operation, the Powertrain Control Module (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 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.
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
The upstream 02S sensor is located before 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 is located near the outlet end of the catalytic converter. 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).
CIRCUIT OPERATION
When the Automatic Shut Down (ASD) relay contacts close, circuit A142 supplies voltage to the upstream and downstream heated oxygen
sensors.
Circuit K41 delivers the signal from the upstream heated oxygen sensor to the Powertrain Control Module (PCM). Circuit K41 connects to cavity
A24 of the PCM. Circuit K141 supplies the signal from the downstream heated oxygen sensor to the PCM. Circuit K141 connects to PCM cavity
A25.
The PCM provides a ground for the heated oxygen sensor signals (circuits K41 and K141) through circuit K4. Circuit K4 connects to cavity A4 of
the PCM connector.
Circuit Z12 provides ground for the heater circuit in each sensor.
