Jeep Grand Cherokee WJ. Manual - part 455

The volume of transmission fluid needed to apply

the friction elements are continuously updated for
adaptive controls. As friction material wears, the vol-
ume of fluid need to apply the element increases.

Certain mechanical problems within the input

clutch assembly (broken return springs, out of posi-
tion snap rings, excessive clutch pack clearance,
improper assembly, etc.) can cause inadequate or out-
of-range element volumes. Also, defective Input/Out-
put Speed Sensors and wiring can cause these
conditions. The following chart identifies the appro-
priate clutch volumes and when they are monitored/
updated:

SHIFT SCHEDULES

As mentioned earlier, the TCM has programming

that allows it to select a variety of shift schedules.
Shift schedule selection is dependent on the follow-
ing:

• Shift lever position

• Throttle position

• Engine load

• Fluid temperature

• Software level
As driving conditions change, the TCM appropri-

ately adjusts the shift schedule. Refer to the follow-
ing chart to determine the appropriate operation
expected, depending on driving conditions.

Schedule

Condition

Expected Operation

Extreme Cold

Oil temperature below -16° F

–Park, Reverse, Neutral and 1st
and 3rd gear only in D position, 2nd
gear only in Manual 2 or L
–No EMCC

Super Cold

Oil temperature between -12° F and
10° F

– Delayed 2-3 upshift
– Delayed 3-4 upshift
– Early 4-3 coastdown shift
– High speed 4-2, 3-2, 2-1 kickdown
shifts are prevented
– Shifts at high throttle openings
willl be early.
– No EMCC

Cold

Oil temperature between 10° F and
36° F

– Shift schedule is the same as
Super Cold except that the 2-3
upshifts are not delayed.

Warm

Oil temperature 40° F and 80° F

– Normal operation (upshift,
kickdowns, and coastdowns)
– No EMCC

Hot

Oil temperature above 80° F and
240° F

– Normal operation (upshift,
kickdowns, and coastdowns)
– Normal EMCC operation

Overheat

Oil temperature above 240° F or
engine coolant temperature above
244° F

– Delayed 2-3 upshift
– Delayed 3-4 upshift
– 3rd gear FEMCC from 30-48 mph
– 3rd gear PEMCC above 35 mph
– Above 25 mph the torque
converter will not unlock unless the
throttle is closed or if a wide open
throttle 2nd PEMCC to 1 kickdown
is made

CLUTCH VOLUMES

Clutch

When Updated

Proper Clutch

Volume

L/R

2-1 or 3-1

downshift

45 to 134

3-2 kickdown

shift

25 to 85

2-3 upshift

30 to 100

3-4 upshift

30 to 85

4-3 kickdown

shift

30 to 100

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DESCRIPTION AND OPERATION (Continued)

SOLENOID AND PRESSURE SWITCH
ASSEMBLY

DESCRIPTION

The solenoid and pressure switch assembly is

internal to the transmission and mounted on the
valve body assembly (Fig. 30). The assembly consists
of six solenoids that control hydraulic pressure to the
six friction elements (transmission clutches), and the
torque converter clutch. The pressure control sole-
noid is located on the side of the solenoid and pres-
sure switch assembly. The solenoid assembly also
contains five pressure switches that feed information
to the TCM.

OPERATION

The solenoids within the assembly are supplied

voltage by the Transmission Control Relay. The sole-
noids are energized when the TCM grounds the
return wire for the solenoid that is needed. The pres-
sure switches simply tell the TCM whether or not
pressure exists within a clutch circuit.

BATTERY FEED (TCM)

DESCRIPTION

A fused, direct battery feed to the TCM is used for

continuous power.

OPERATION

This battery voltage is necessary to retain adaptive

learn values in the TCM’s RAM (Random Access
Memory). When the battery (B+) is disconnected, this
memory is lost. When the battery (B+) is restored,

this memory loss is detected by the TCM and a Diag-
nostic Trouble Code (DTC) is set.

TRANSMISSION CONTROL RELAY

DESCRIPTION

The relay is supplied fused B+ voltage, energized

by the TCM, and is used to supply power to the sole-
noid pack when the transmission is in normal oper-
ating mode.

OPERATION

When the relay is “off”, no power is supplied to the

solenoid pack and the transmission is in “limp-in”
mode. After a controller reset, the TCM energizes the
relay. Prior to this, the TCM verifies that the con-
tacts are open by checking for no voltage at the
switched battery terminals. After this is verified, the
voltage at the solenoid pack pressure switches is
checked. After the relay is energized, the TCM mon-
itors the terminals to verify that the voltage is
greater than 3 volts.

PRESSURE SWITCHES

DESCRIPTION

The pressure switches are located inside the sole-

noid and pressure switch assembly and are only ser-
viced by replacing the assembly.

OPERATION

The TCM relies on five pressure switches to moni-

tor fluid pressure in the L/R, 2C, 4C, UD, and OD
hydraulic circuits. The primary purpose of these
switches is to help the TCM detect when clutch cir-
cuit hydraulic failures occur. The switches close at 23
psi and open at 11 psi, and simply indicate whether
or not pressure exists. The switches are continuously
monitored by the TCM for the correct states (open or
closed) in each gear as shown in the following chart:

Fig. 30 SOLENOID AND PRESSURE SWITCH

ASSEMBLY

GEAR

L/R

P/N

1ST

CL*

2ND

PRIME

*L/R is closed if output speed is below 100 rpm in

Drive and Manual 2. L/R is open in Manual 1.

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DESCRIPTION AND OPERATION (Continued)

A Diagnostic Trouble Code (DTC) will set if the

TCM senses any switch open or closed at the wrong
time in a given gear.

INPUT AND OUTPUT SPEED SENSORS

DESCRIPTION

The Input and Output Speed Sensors are two-wire

magnetic pickup devices that generate AC signals as
rotation occurs. They are mounted in the left side of
the transmission case and are considered primary
inputs to the Transmission Control Module (TCM).

OPERATION

The Input Speed Sensor provides information on

how fast the input shaft is rotating. As the teeth of
the input clutch hub pass by the sensor coil, an AC
voltage is generated and sent to the TCM. The TCM
interprets this information as input shaft rpm.

The Output Speed Sensor generates an AC signal

in a similar fashion, though its coil is excited by rota-
tion of the rear planetary carrier lugs. The TCM
interprets this information as output shaft rpm.

The TCM compares the input and output speed

signals to determine the following:

• Transmission gear ratio

• Speed ratio error detection

• CVI calculation
The TCM also compares the input speed signal and

the engine speed signal to determine the following:

• Torque converter clutch slippage

• Torque converter element speed ratio

LINE PRESSURE CONTROL

DESCRIPTION

The TCM utilizes a closed-loop system to control

transmission line pressure. The system contains a
variable force style solenoid, the Pressure Control
Solenoid, mounted on the side of the solenoid and
pressure switch assembly. The solenoid is duty cycle
controlled by the TCM to vent the unnecessary line
pressure supplied by the oil pump back to the sump.
The system also contains a variable pressure style
sensor, the Line Pressure Sensor, which is a direct
input to the TCM. The line pressure solenoid moni-
tors the transmission line pressure and completes the
feedback loop to the TCM. The TCM uses this infor-
mation to adjust its control of the pressure control
solenoid to achieve the desired line pressure.

OPERATION

The TCM calculates the desired line pressure

based upon inputs from the transmission and engine.
The TCM calculates the torque input to the trans-
mission and uses that information as the primary

input to the calculation. The line pressure is set to a
predetermined value during shifts and when the
transmission is in the PARK and NEUTRAL posi-
tions. This is done to ensure consistent shift quality.
During all other operation, the actual line pressure is
compared to the desired line pressure and adjust-
ments are made to the pressure control solenoid duty
cycle.

THROTTLE POSITION SENSOR

OPERATION

The Transmission Control Module (TCM) receives

the throttle position signal and its ground from the
Throttle Position Sensor (TPS). The TPS has a 5 volt
pull up supplied by the engine controller. The throt-
tle signal is checked by the TCM for out-of-range as
well as intermittence (excessive signal changes).

TRANSMISSION RANGE SENSOR

DESCRIPTION

The Transmission Range Sensor (TRS) is mounted

to the top of the valve body inside the transmission.

The Transmission Range Sensor (TRS) has six

switch contacts that:

• Determine shift lever position

• Supply ground to the Starter Relay in Park and

Neutral only.

• Supply ground to the TCM for backup lamp con-

trol in Reverse only.

The TRS also has an integrated temperature sen-

sor (thermistor) that communicates transmission
temperature to the TCM and PCM.

OPERATION

The Transmission Range Sensor (TRS) communi-

cates shift lever position to the TCM as a combina-
tion of open and closed switches. Each shift lever
position has an assigned combination of switch states
(open/closed) that the TCM receives from four sense
circuits. The TCM interprets this information and
determines the appropriate transmission gear posi-
tion and shift schedule.

There are many possible combinations of open and

closed switches (codes). Seven of these possible codes
are related to gear position and five are recognized
as “between gear” codes. This results in many codes
which

should

never

occur.

These

are

called

“invalid” codes. An invalid code will result in a DTC,
and the TCM will then determine the shift lever
position based on pressure switch data. This allows
reasonably normal transmission operation with a
TRS failure.

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45RFE AUTOMATIC TRANSMISSION

DESCRIPTION AND OPERATION (Continued)

TRANSMISSION TEMPERATURE SENSOR

DESCRIPTION

The transmission temperature sensor is a ther-

mistor that is integral to the Transmission Range
Sensor (TRS).

OPERATION

The transmission temperature sensor is used by

the TCM to sense the temperature of the fluid in the
sump. Since fluid temperature can affect transmis-
sion shift quality and convertor lock up, the TCM
requires this information to determine which shift
schedule to operate in.

Calculated Temperature

A failure in the temperature sensor or circuit will

result in calculated temperature being substituted for
actual temperature. Calculated temperature is a pre-
dicted fluid temperature which is calculated from a
combination of inputs:

• Battery (ambient) temperature

• Engine coolant temperature

• In-gear run time since start-up

SOLENOIDS

DESCRIPTION

Solenoids are used to control the L/R, 2C, 4C, OD,

and UD friction elements. The reverse clutch is con-
trolled by line pressure and the position of the man-
ual valve in the valve body. All the solenoids are
contained within the Solenoid and Pressure Switch
Assembly. The solenoid and pressure switch assembly
contains one additional solenoid, Multi-Select (MS),
which serves primarily to provide 2nd and 3rd gear
limp-in operation.

OPERATION

The solenoids receive electrical power from the

Transmission Control Relay through a single wire.
The TCM energizes or operates the solenoids individ-
ually by grounding the return wire of the solenoid as
necessary. When a solenoid is energized, the solenoid
valve shifts, and a fluid passage is opened or closed
(vented or applied), depending on its default operat-
ing state. The result is an apply or release of a fric-
tional element.

The MS and UD solenoids are normally applied to

allow transmission limp-in in the event of an electri-
cal failure.

The continuity of the solenoids and circuits are

periodically tested. Each solenoid is turned on or off
depending on its current state. An inductive spike
should be detected by the TCM during this test. If no
spike is detected, the circuit is tested again to verify
the failure. In addition to the periodic testing, the
solenoid circuits are tested if a speed ratio or pres-
sure switch error occurs.

SOLENOID SWITCH VALVE

DESCRIPTION

The Solenoid Switch Valve (SSV) is located in the

valve body controls the direction of the transmission
fluid when the L/R-TCC solenoid is energized.

OPERATION

The Solenoid Switch Valve controls line pressure

from the LR-TCC solenoid. In 1st gear, the SSV will
be in the downshifted position, thus directing fluid to
the L/R clutch circuit. In 2nd, 3rd, and 4th, it will be
in the upshifted position and directs the fluid into
the torque converter clutch (TCC) circuit.

When shifting into 1st gear, a special hydraulic

sequence is performed to ensure SSV movement into
the downshifted position. The L/R pressure switch is
monitored to confirm SSV movement. If the move-
ment is not confirmed (the L/R pressure switch does
not close), 2nd gear is substituted for 1st. A DTC will
be set after three unsuccessful attempts are made to
get into 1st gear in one given key start.

DIAGNOSIS AND TESTING

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-

GEAR

Park

Temp 1

Reverse

Temp 2

Neutral 1

Neutral 2

Temp 3

Drive

Temp 4

Manual 2

Temp 5

Manual 1

45RFE AUTOMATIC TRANSMISSION

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DESCRIPTION AND OPERATION (Continued)

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