Jeep 1996 Grand Cherokee Service Manual - page 1145
POWERTRAIN CONTROL MODULE (PCM)
The PCM controls operation of the converter
clutch, overdrive clutch, and governor pressure sole-
noid.
The control module determines transmission shift
points based on input signals from the transmission
thermistor, transmission output shaft speed sensor,
crankshaft position sensor, vehicle speed sensor, and
throttle position sensor.
Operating voltage is supplied through the battery
terminal on the control module. The ignition voltage
signal is supplied through a terminal on the ABS
control module.
The DRB scan tool can be used to check operation
of the control module and transmission electrical
components. The diagnostic connector (for the scan
tool) is located under the instrument panel near the
steering column. The connector has a 6-way terminal
and is blue in color.
GOVERNOR PRESSURE CURVES
There are four governor pressure curves pro-
grammed into the transmission control module. The
different curves allow the control module to adjust
governor pressure for varying conditions. One curve
is used for operation when fluid temperature is at, or
below, 1°C (30°F). A second curve is used when fluid
temperature is at, or above, 10°C (50°F) during nor-
mal city or highway driving. A third curve is used
during wide-open throttle operation. The fourth curve
is used when driving with the transfer case in low
range.
SHIFT VALVE OPERATION
The shift valves are moved by a combination of
throttle and governor pressure. The governor pres-
sure is generated by electrical components.
The conditions under which a shift to fourth will
not occur when:
• Overdrive switch is Off
• Transmission fluid temperature is below 10° C
(50° F) or above 121° C (250° F)
• Shift to third not yet completed
• Vehicle speed too low for 3-4 shift to occur
HYDRAULIC CONTROL SYSTEM
The hydraulic control system provides fully auto-
matic operation. The system performs five basic func-
tions which are: pressure supply, pressure regulation,
flow control, clutch/band application, and lubrication.
PRESSURE REGULATION
The pressure regulator valve maintains line pres-
sure. The amount of pressure developed is controlled
by throttle pressure which is dependent on the
degree of throttle opening. The regulator valve is
located in the valve body.
The throttle valve determines line pressure and
shift speed. Governor pressure increases in propor-
tion to vehicle speed. The throttle valve controls
upshift and downshift speeds by regulating pressure
according to throttle position.
Shift Valve Flow Control
The manual valve is operated by the gearshift link-
age and provides the operating range selected by the
driver.
The 1-2 shift valve provides 1-2 or 2-1 shifts and
the 2-3 shift valve provides 2-3 or 3-2 shifts.
The kickdown valve provides forced 3-2 or 3-1
downshifts depending on vehicle speed. Downshifts
occur when the throttle is opened beyond downshift
detent position. Detent is reached just before wide
open throttle position.
The 2-3 valve throttle pressure plug provides 3-2
downshifts at varying throttle openings depending on
vehicle speed.
Fig. 5 Thermistor Location
Fig. 6 Transmission Speed Sensor
21 - 6
TRANSMISSION AND TRANSFER CASE
ZJ
DESCRIPTION AND OPERATION (Continued)