Grand Cherokee 2WD L6-4.0L VIN S (1997)
Output Shaft Speed Sensor
OUTPUT SHAFT SPEED SENSOR-PCM INPUT
This sensor generates a signal to the Powertrain Control Module (PCM) relating to the speed of the transmission main drive shaft. This input is
used with 4-speed electronic transmissions only.
Overdrive/Override Switch
OVERDRIVE/OVERRIDE SWITCH-PCM INPUT
On vehicles equipped with an automatic transmission and overdrive, the Powertrain Control Module (PCM) regulates the 3-4 overdrive up-shift
and downshift through the overdrive solenoid. This solenoid is located in the transmission. An overdrive/override push-button switch is located on
the instrument panel.
The overdrive/override push-button switch is normally open (overdrive allowed) when the lamp is not illuminated. It momentarily closes
(overdrive not allowed) when the operator presses the switch and the lamp is illuminated. Overdrive will revert to ON (lamp off) each time the
ignition switch in turned on. The transmission downshifts if the operator presses the override switch while in overdrive.
Oxygen Sensors (02S)
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).
Sensor Return
SENSOR RETURN-PCM INPUT
Sensor Return provides a low noise ground reference for all system sensors.
Signal Ground
SIGNAL GROUND-PCM INPUT
Signal ground provides a low noise ground to the data link connector.
Speed Control Switches
