Specifications

I've got Four (4) O2 Sensors...What do they do?
OXYGEN SENSOR-PCM INPUTS
When the vehicle is equipped with a this engine and two-wheel-drive (2WD), four heated O2S sensors Will
be used. 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.
Two of these sensors are installed into the left and right exhaust manifold down pipes. The left O2S sensor
will monitor cylinders 1, 3, 5 and 7. The right sensor will monitor cylinders 2, 4, 6 and 8.
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
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 converter efficiency.
POST CATALYST OXYGEN SENSOR
The post catalyst heated oxygen sensor threads into the outlet end of the catalytic converter. The post
catalyst heated oxygen sensor input is used to detect catalytic converter deterioration and fine tune the air
fuel ratio. As the converter deteriorates, the input from this sensor begins to match the pre-catalyst sensor
input except for a slight time delay. By comparing the inputs from both of these sensors, the PCM
calculates catalytic converter efficiency.
When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic
trouble code and illuminates the Malfunction Indicator Lamp (MIL).