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Dodge Durango (DN). Manual - part 44

GOVERNOR PRESSURE SENSOR

The governor pressure sensor measures output

pressure of the governor pressure solenoid valve (Fig.
64).

GOVERNOR BODY AND TRANSFER PLATE

The transfer plate is designed to supply transmis-

sion line pressure to the governor pressure solenoid
valve and to return governor pressure.

The governor pressure solenoid valve is mounted in

the governor body. The body is bolted to the lower
side of the transfer plate (Fig. 64).

TRANSMISSION FLUID TEMPERATURE THERMISTOR

Transmission fluid temperature readings are sup-

plied to the transmission control module by the ther-
mistor. The temperature readings are used to control
engagement of the fourth gear overdrive clutch, the
converter clutch, and governor pressure. Normal
resistance value for the thermistor at room tempera-
ture is approximately 1000 ohms.

The thermistor is part of the governor pressure

sensor assembly and is immersed in transmission
fluid at all times.

TRANSMISSION SPEED SENSOR

The speed sensor (Fig. 65) is located in the over-

drive gear case. The sensor is positioned over the
park gear and monitors transmission output shaft
rotating speed.

OPERATION

Compensation is required for performance varia-

tions of two of the input devices. Though the slope of
the transfer functions is tightly controlled, offset may
vary due to various environmental factors or manu-
facturing tolerances.

The pressure transducer is affected by barometric

pressure as well as temperature. Calibration of the
zero pressure offset is required to compensate for
shifting output due to these factors.

Normal calibration will be performed when sump

temperature is above 50 degrees F, or in the absence
of sump temperature data, after the first 10 minutes
of vehicle operation. Calibration of the pressure
transducer offset occurs each time the output shaft
speed falls below 200 RPM. Calibration shall be
repeated each 3 seconds the output shaft speed is
below 200 RPM. A.5 second pulse of 95% duty cycle
is applied to the governor pressure solenoid valve
and the transducer output is read during this pulse.
Averaging of the transducer signal is necessary to
reject electrical noise.

Under cold conditions (below 50 degrees F sump),

the governor pressure solenoid valve response may
be too slow to guarantee 0 psi during the.5 second
calibration pulse. Calibration pulses are continued
during this period, however the transducer output
valves are discarded. Transducer offset must be read
at key-on, under conditions which promote a stable
reading. This value is retained and becomes the off-
set during the “cold” period of operation.

Fig. 63 Governor Pressure Solenoid Valve

1 – SOLENOID FILTER
2 – GOVERNOR PRESSURE SOLENOID

Fig. 64 Governor Pressure Sensor

1 – GOVERNOR BODY
2 – GOVERNOR PRESSURE SENSOR/TRANSMISSION FLUID

TEMPERATURE THERMISTOR

Fig. 65 Transmission Output Speed Sensor

1 – TRANSMISSION OUTPUT SHAFT SPEED SENSOR
2 – SEAL

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DESCRIPTION AND OPERATION (Continued)

GOVERNOR PRESSURE SOLENOID VALVE

The inlet side of the solenoid valve is exposed to

normal transmission line pressure. The outlet side of
the valve leads to the valve body governor circuit.

The solenoid valve regulates line pressure to pro-

duce governor pressure. The average current sup-
plied to the solenoid controls governor pressure. One
amp current produces zero kPa/psi governor pres-
sure. Zero amps sets the maximum governor pres-
sure.

The powertrain control module (PCM) turns on the

trans control relay which supplies electrical power to
the solenoid valve. Operating voltage is 12 volts
(DC). The PCM controls the ground side of the sole-
noid using the governor pressure solenoid control cir-
cuit.

GOVERNOR PRESSURE SENSOR

The sensor output signal provides the necessary

feedback to the PCM. This feedback is needed to ade-
quately control governor pressure.

GOVERNOR BODY AND TRANSFER PLATE

The transfer plate channels line pressure to the

solenoid valve through the governor body. It also
channels governor pressure from the solenoid valve
to the governor circuit. It is the solenoid valve that
develops the necessary governor pressure.

TRANSMISSION FLUID TEMPERATURE THERMISTOR

The PCM prevents engagement of the converter

clutch and overdrive clutch, when fluid temperature
is below approximately 10°C (50°F).

If fluid temperature exceeds 126°C (260°F), the

PCM causes a 4-3 downshift and engage the con-
verter clutch. Engagement is according to the third
gear converter clutch engagement schedule.

The overdrive OFF lamp in the instrument panel

illuminates when the shift back to third occurs. The
transmission will not allow fourth gear operation
until fluid temperature decreases to approximately
110°C (230°F).

TRANSMISSION SPEED SENSOR

Speed sensor signals are triggered by the park

gear lugs as they rotate past the sensor pickup face.
Input signals from the sensor are sent to the trans-
mission control module for processing. The vehicle
speed sensor also serves as a backup for the trans-
mission speed sensor. Signals from this sensor are
shared with the powertrain control module.

GOVERNOR PRESSURE CURVES

DESCRIPTION

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.

OPERATION

LOW TRANSMISSION FLUID TEMPERATURE

When the transmission fluid is cold the conven-

tional governor can delay shifts, resulting in higher
than normal shift speeds and harsh shifts. The elec-
tronically controlled low temperature governor pres-
sure curve is higher than normal to make the
transmission shift at normal speeds and sooner. The
PCM uses a temperature sensor in the transmission
oil sump to determine when low temperature gover-
nor pressure is needed.

NORMAL OPERATION

Normal operation is refined through the increased

computing power of the PCM and through access to
data on engine operating conditions provided by the
PCM that were not available with the previous
stand-alone electronic module. This facilitated the
development of a load adaptive shift strategy - the
ability to alter the shift schedule in response to vehi-
cle load condition. One manifestation of this capabil-
ity is grade “hunting” prevention - the ability of the
transmission logic to delay an upshift on a grade if
the engine does not have sufficient power to main-
tain speed in the higher gear. The 3-2 downshift and
the potential for hunting between gears occurs with a
heavily loaded vehicle or on steep grades. When
hunting occurs, it is very objectionable because shifts
are frequent and accompanied by large changes in
noise and acceleration.

WIDE OPEN THROTTLE OPERATION

In wide-open throttle (WOT) mode, adaptive mem-

ory in the PCM assures that up-shifts occur at the
preprogrammed optimum speed. WOT operation is
determined from the throttle position sensor, which
is also a part of the emission control system. The ini-
tial setting for the WOT upshift is below the opti-
mum engine speed. As WOT shifts are repeated, the
PCM learns the time required to complete the shifts

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DESCRIPTION AND OPERATION (Continued)

by comparing the engine speed when the shifts occur
to the optimum speed. After each shift, the PCM
adjusts the shift point until the optimum speed is
reached. The PCM also considers vehicle loading,
grade and engine performance changes due to high
altitude in determining when to make WOT shifts. It
does this by measuring vehicle and engine accelera-
tion and then factoring in the shift time.

TRANSFER CASE LOW RANGE OPERATION

On four-wheel drive vehicles operating in low

range, the engine can accelerate to its peak more
rapidly than in Normal range, resulting in delayed
shifts and undesirable engine “flare.” The low range
governor pressure curve is also higher than normal
to initiate upshifts sooner. The PCM compares elec-
tronic vehicle speed signal used by the speedometer
to the transmission output shaft speed signal to
determine when the transfer case is in low range.

OVERDRIVE OFF SWITCH

DESCRIPTION

The overdrive OFF (control) switch is located in

the shift lever arm.

OPERATION

The switch is a momentary contact device that sig-

nals the PCM to toggle current status of the over-
drive function. At key-on, overdrive operation is
allowed. Pressing the switch once causes the over-
drive OFF mode to be entered and the overdrive OFF
switch lamp to be illuminated. Pressing the switch a
second time causes normal overdrive operation to be
restored and the overdrive lamp to be turned off. The
overdrive OFF mode defaults to ON after the ignition
switch is cycled OFF and ON. The normal position
for the control switch is the ON position. The switch
must be in this position to energize the solenoid and
allow a 3-4 upshift. The control switch indicator light
illuminates only when the overdrive switch is turned
to the OFF position, or when illuminated by the
transmission control module.

DIAGNOSIS AND TESTING

AUTOMATIC TRANSMISSION DIAGNOSIS

Automatic transmission problems can be a result of

poor engine performance, incorrect fluid level, incor-
rect linkage or cable adjustment, band or hydraulic
control pressure adjustments, hydraulic system mal-
functions or electrical/mechanical component mal-
functions. Begin diagnosis by checking the easily
accessible items such as: fluid level and condition,
linkage adjustments and electrical connections. A

road test will determine if further diagnosis is neces-
sary.

EFFECTS OF INCORRECT FLUID LEVEL

A low fluid level allows the pump to take in air

along with the fluid. Air in the fluid will cause fluid
pressures to be low and develop slower than normal.
If the transmission is overfilled, the gears churn the
fluid into foam. This aerates the fluid and causing
the same conditions occurring with a low level. In
either case, air bubbles cause fluid overheating, oxi-
dation and varnish buildup which interferes with
valve, clutch and servo operation. Foaming also
causes fluid expansion which can result in fluid over-
flow from the transmission vent or fill tube. Fluid
overflow can easily be mistaken for a leak if inspec-
tion is not careful.

CAUSES OF BURNT FLUID

Burnt, discolored fluid is a result of overheating

which has two primary causes.

(1) A result of restricted fluid flow through the

main and/or auxiliary cooler. This condition is usu-
ally the result of a faulty or improperly installed
drainback valve, a damaged main cooler, or severe
restrictions in the coolers and lines caused by debris
or kinked lines.

(2) Heavy duty operation with a vehicle not prop-

erly equipped for this type of operation. Trailer tow-
ing or similar high load operation will overheat the
transmission

fluid

the

vehicle

improperly

equipped. Such vehicles should have an auxiliary
transmission fluid cooler, a heavy duty cooling sys-
tem, and the engine/axle ratio combination needed to
handle heavy loads.

FLUID CONTAMINATION

Transmission fluid contamination is generally a

result of:

• adding incorrect fluid

• failure to clean dipstick and fill tube when

checking level

• engine coolant entering the fluid

• internal failure that generates debris

• overheat that generates sludge (fluid break-

down)

• failure to reverse flush cooler and lines after

repair

• failure to replace contaminated converter after

repair

The use of non recommended fluids can result in

transmission failure. The usual results are erratic
shifts, slippage, abnormal wear and eventual failure
due to fluid breakdown and sludge formation. Avoid
this condition by using recommended fluids only.

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DESCRIPTION AND OPERATION (Continued)

The dipstick cap and fill tube should be wiped

clean before checking fluid level. Dirt, grease and
other foreign material on the cap and tube could fall
into the tube if not removed beforehand. Take the
time to wipe the cap and tube clean before withdraw-
ing the dipstick.

Engine coolant in the transmission fluid is gener-

ally caused by a cooler malfunction. The only remedy
is to replace the radiator as the cooler in the radiator
is not a serviceable part. If coolant has circulated
through the transmission for some time, an overhaul
may also be necessary; especially if shift problems
had developed.

The transmission cooler and lines should be

reverse flushed whenever a malfunction generates
sludge and/or debris. The torque converter should
also be replaced at the same time.

Failure to flush the cooler and lines will result in

recontamination. Flushing applies to auxiliary cool-
ers as well. The torque converter should also be
replaced whenever a failure generates sludge and
debris. This is necessary because normal converter
flushing procedures will not remove all contami-
nants.

PRELIMINARY DIAGNOSIS

Two basic procedures are required. One procedure

for vehicles that are drivable and an alternate proce-
dure for disabled vehicles (will not back up or move
forward).

VEHICLE IS DRIVEABLE

(1) Check for transmission fault codes using DRB

scan tool.

(2) Check fluid level and condition.
(3) Adjust throttle and gearshift linkage if com-

plaint was based on delayed, erratic, or harsh shifts.

(4) Road test and note how transmission upshifts,

downshifts, and engages.

(5) Perform stall test if complaint is based on slug-

gish acceleration. Or, if abnormal throttle opening is
needed to maintain normal speeds with a properly
tuned engine.

(6) Perform hydraulic pressure test if shift prob-

lems were noted during road test.

(7) Perform air-pressure test to check clutch-band

operation.

VEHICLE IS DISABLED

(1) Check fluid level and condition.
(2) Check for broken or disconnected gearshift or

throttle linkage.

(3) Check for cracked, leaking cooler lines, or loose

or missing pressure-port plugs.

(4) Raise and support vehicle on safety stands,

start engine, shift transmission into gear, and note
following:

(a) If propeller shaft turns but wheels do not,

problem is with differential or axle shafts.

(b) If propeller shaft does not turn and transmis-

sion is noisy, stop engine. Remove oil pan, and
check for debris. If pan is clear, remove transmis-
sion and check for damaged drive plate, converter,
oil pump, or input shaft.

sion is not noisy, perform hydraulic-pressure test to
determine if problem is hydraulic or mechanical.

PARK/NEUTRAL POSITION SWITCH

The center terminal of the park/neutral position

switch is the starter-circuit terminal. It provides the
ground for the starter solenoid circuit through the
selector lever in PARK and NEUTRAL positions only.
The outer terminals on the switch are for the backup
lamp circuit.

SWITCH TEST

To test the switch, remove the wiring connector.

Test for continuity between the center terminal and
the transmission case. Continuity should exist only
when the transmission is in PARK or NEUTRAL.

Shift the transmission into REVERSE and test

continuity at the switch outer terminals. Continuity
should exist only when the transmission is in
REVERSE. Continuity should not exist between the
outer terminals and the case.

Check gearshift linkage adjustment before replac-

ing a switch that tests faulty.

OVERDRIVE ELECTRICAL CONTROLS

The overdrive off switch, valve body solenoid, case

connectors and related wiring can all be tested with
a 12 volt test lamp or a volt/ohmmeter. Check conti-
nuity of each component when diagnosis indicates
this is necessary. Refer to Group 8W, Wiring Dia-
grams, for component locations and circuit informa-
tion.

Switch and solenoid continuity should be checked

whenever the transmission fails to shift into fourth
gear range.

GEARSHIFT CABLE

(1) The shifter lever and gate positions should be

in alignment with all transmission PARK, NEU-
TRAL, and gear detent positions.

(2) Engine starts must be possible with shift lever

in PARK or NEUTRAL gate positions only. Engine
starts must not be possible in any other gear posi-
tion.

(3) With shift lever handle in:

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DIAGNOSIS AND TESTING (Continued)

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