Dodge Durango (DN). Manual — part 84

OPERATION

KICKDOWN (FRONT) SERVO

The application of the piston is accomplished by

applying pressure between the two lands of the pis-
ton. The pressure acts against the larger lower land
to push the piston downward, allowing the piston rod
to extend though its guide against the apply lever.
Release of the servo at the 2–3 upshift is accom-
plished by a combination of spring and line pressure,
acting on the bottom of the larger land of the piston.
The small piston is used to cushion the application of
the band by bleeding oil through a small orifice in
the larger piston. The release timing of the kickdown
servo is very important to obtain a smooth but firm
shift. The release has to be very quick, just as the
front clutch application is taking place. Otherwise,
engine runaway or a shift hesitation will occur. To
accomplish this, the band retains its holding capacity
until the front clutch is applied, giving a small
amount of overlap between them.

LOW/REVERSE (REAR) SERVO

While in the de-energized state (no pressure

applied), the piston is held up in its bore by the pis-
ton spring. The plug is held down in its bore, in the
piston, by the plug spring. When pressure is applied
to the top of the piston, the plug is forced down in its
bore, taking up any clearance. As the piston moves, it
causes the plug spring to compress, and the piston
moves down over the plug. The piston continues to
move down until it hits the shoulder of the plug and
fully applies the band. The period of time from the
initial application, until the piston is against the
shoulder of the plug, represents a reduced shocking
of the band that cushions the shift.

GEARSHIFT MECHANISM

DESCRIPTION

The gear shift mechanism provides six shift posi-

tions which are:

• Park (P)

• Reverse (R)

• Neutral (N)

• Drive (D)

• Manual second (2)

• Manual low (1)

OPERATION

Manual low (1) range provides first gear only.

Overrun braking is also provided in this range. Man-
ual second (2) range provides first and second gear
only.

Drive range provides first, second third and over-

drive fourth gear ranges. The shift into overdrive

fourth gear range occurs only after the transmission
has completed the shift into D third gear range. No
further movement of the shift mechanism is required
to complete the 3-4 shift.

The fourth gear upshift occurs automatically when

the overdrive selector switch is in the ON position.
No upshift to fourth gear will occur if any of the fol-
lowing are true:

• The transmission fluid temperature is below 10°

C (50° F) or above 121° C (250° F).

• The shift to third is not yet complete.

• Vehicle speed is too low for the 3–4 shift to

occur.

• Battery temperature is below –5° C (23° F).

CONVERTER DRAINBACK VALVE

DESCRIPTION

The drainback valve is located in the transmission

cooler outlet (pressure) line.

OPERATION

The valve prevents fluid from draining from the

converter into the cooler and lines when the vehicle
is shut down for lengthy periods. Production valves
have a hose nipple at one end, while the opposite end
is threaded for a flare fitting. All valves have an
arrow (or similar mark) to indicate direction of flow
through the valve.

POWERTRAIN CONTROL MODULE (PCM)

DESCRIPTION

The Powertrain Control Module (PCM) is located

in the engine compartment (Fig. 62). The PCM is
referred to as JTEC.

OPERATION

The PCM operates the fuel system. The PCM is a

pre-programmed, triple microprocessor digital com-
puter. It regulates ignition timing, air-fuel ratio,
emission control devices, charging system, certain
transmission features, speed control, air conditioning
compressor clutch engagement and idle speed. The
PCM can adapt its programming to meet changing
operating conditions.

The PCM receives input signals from various

switches and sensors. Based on these inputs, the
PCM regulates various engine and vehicle operations
through different system components. These compo-
nents are referred to as Powertrain Control Module
(PCM) Outputs. The sensors and switches that pro-
vide inputs to the PCM are considered Powertrain
Control Module (PCM) Inputs.

The PCM adjusts ignition timing based upon

inputs it receives from sensors that react to: engine

21 - 202

46RE AUTOMATIC TRANSMISSION

DN

DESCRIPTION AND OPERATION (Continued)

rpm, manifold absolute pressure, engine coolant tem-
perature, throttle position, transmission gear selec-
tion (automatic transmission), vehicle speed and the
brake switch.

The PCM adjusts idle speed based on inputs it

receives from sensors that react to: throttle position,
vehicle speed, transmission gear selection, engine
coolant temperature and from inputs it receives from
the air conditioning clutch switch and brake switch.

Based on inputs that it receives, the PCM adjusts

ignition coil dwell. The PCM also adjusts the gener-
ator charge rate through control of the generator
field and provides speed control operation.

NOTE: PCM Inputs:

• A/C request (if equipped with factory A/C)

• A/C select (if equipped with factory A/C)

• Auto shutdown (ASD) sense

• Battery temperature

• Battery voltage

• Brake switch

• CCD bus (+) circuits

• CCD bus (-) circuits

• Camshaft position sensor signal

• Crankshaft position sensor

• Data link connection for DRB scan tool

• Engine coolant temperature sensor

• Fuel level

• Generator (battery voltage) output

• Ignition circuit sense (ignition switch in on/off/

crank/run position)

• Intake manifold air temperature sensor

• Leak detection pump (switch) sense (if equipped)

• Manifold absolute pressure (MAP) sensor

• Oil pressure

• Output shaft speed sensor

• Overdrive/override switch

• Oxygen sensors

• Park/neutral switch (auto. trans. only)

• Power ground

• Sensor return

• Signal ground

• Speed control multiplexed single wire input

• Throttle position sensor

• Transmission governor pressure sensor

• Transmission temperature sensor

• Vehicle speed inputs from ABS or RWAL system

NOTE: PCM Outputs:

• A/C clutch relay

• Auto shutdown (ASD) relay

• CCD bus (+/-) circuits for: speedometer, voltme-

ter, fuel gauge, oil pressure gauge/lamp, engine temp.
gauge and speed control warn. lamp

• Data link connection for DRB scan tool

• EGR valve control solenoid (if equipped)

• EVAP canister purge solenoid

• Five volt sensor supply (primary)

• Five volt sensor supply (secondary)

• Fuel injectors

• Fuel pump relay

• Generator field driver (-)

• Generator field driver (+)

• Generator lamp (if equipped)

• Idle air control (IAC) motor

• Ignition coil

• Leak detection pump (if equipped)

• Malfunction indicator lamp (Check engine lamp).

Driven through CCD circuits.

• Overdrive indicator lamp (if equipped)

• Radiator cooling fan (2.5L engine only)

• Speed control vacuum solenoid

• Speed control vent solenoid

• Tachometer (if equipped). Driven through CCD

circuits.

• Transmission convertor clutch circuit

• Transmission 3–4 shift solenoid

• Transmission relay

• Transmission temperature lamp (if equipped)

• Transmission variable force solenoid

Fig. 62 PCM Location

1 – RIGHT FRONT FENDER
2 – PCM MOUNTING BOLTS (3)
3 – 32–WAY CONNECTORS (3)
4 – COVER
5 – POWERTRAIN CONTROL MODULE (PCM)

DN

46RE AUTOMATIC TRANSMISSION

21 - 203

DESCRIPTION AND OPERATION (Continued)

ELECTRONIC GOVERNOR

DESCRIPTION

Governor pressure is controlled electronically. Com-

ponents used for governor pressure control include:

• Governor body

• Valve body transfer plate

• Governor pressure solenoid valve

• Governor pressure sensor

• Fluid temperature thermistor

• Throttle position sensor (TPS)

• Transmission speed sensor

• Powertrain control module (PCM)

GOVERNOR PRESSURE SOLENOID VALVE

The solenoid valve is a duty-cycle solenoid which

regulates the governor pressure needed for upshifts
and downshifts. It is an electro-hydraulic device
located in the governor body on the valve body trans-
fer plate (Fig. 63).

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

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

21 - 204

46RE AUTOMATIC TRANSMISSION

DN

DESCRIPTION AND OPERATION (Continued)

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.

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

DN

46RE AUTOMATIC TRANSMISSION

21 - 205

DESCRIPTION AND OPERATION (Continued)