Dodge Durango (DN). Manual — part 120
TRANSMISSION CONTROL MODULE
DESCRIPTION
The Transmission Control Module (TCM) is located
in the engine compartment on the right (passenger)
side and is mounted to the radiator core support (Fig.
27).
OPERATION
The TCM is the controlling unit for all electronic
operations of the transmission. The TCM receives
information regarding vehicle operation from both
direct and indirect inputs, and selects the operational
mode of the transmission. Direct inputs are hard-
wired to, and used specifically by the TCM. Indirect
inputs originate from other components/modules, and
are shared with the TCM via the vehicle communica-
tion bus.
Some examples of direct inputs to the TCM are:
• Battery (B+) voltage
• Ignition “ON” voltage
• Transmission Control Relay (Switched B+)
• Throttle Position Sensor
• Crankshaft Position Sensor
• Transmission Range Sensor
• Pressure Switches
• Transmission Temperature Sensor
• Input Shaft Speed Sensor
• Output Shaft Speed Sensor
• Line Pressure Sensor
Some examples of indirect inputs to the TCM
are:
• Engine/Body Identification
• Manifold Pressure
• Target Idle
• Torque Reduction Confirmation
• Engine Coolant Temperature
• Ambient/Battery Temperature
• DRB Scan Tool Communication
Based on the information received from these var-
ious inputs, the TCM determines the appropriate
shift schedule and shift points, depending on the
present operating conditions and driver demand.
This is possible through the control of various direct
and indirect outputs.
Some examples of TCM direct outputs are:
• Transmission Control Relay
• Solenoids
Fig. 25 Reaction Planetary Geartrain
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DESCRIPTION AND OPERATION (Continued)
• Torque Reduction Request
Some examples of TCM indirect outputs are:
• Transmission Temperature (to PCM)
• PRNDL Position (to BCM)
In addition to monitoring inputs and controlling
outputs, the TCM has other important responsibili-
ties and functions:
• Storing and maintaining Clutch Volume Indexes
(CVI)
• Storing and selecting appropriate Shift Sched-
ules
• System self-diagnostics
• Diagnostic capabilities (with DRB scan tool)
NOTE: If the TCM has been replaced, the “Quick
Learn Procedure” must be performed. Refer to
“Quick Learn Procedure” in Service Procedures of
this group.
CLUTCH VOLUME INDEXES
An important function of the TCM is to monitor
Clutch Volume Indexes (CVI). CVIs represent the vol-
ume of fluid needed to compress a clutch pack.
The TCM monitors gear ratio changes by monitor-
ing the Input and Output Speed Sensors. The Input,
or Turbine Speed Sensor sends an electrical signal to
the TCM that represents input shaft rpm. The Out-
put Speed Sensor provides the TCM with output
shaft speed information.
By comparing the two inputs, the TCM can deter-
mine transmission gear position. This is important to
the CVI calculation because the TCM determines
Fig. 26 Reverse/Input Planetary Geartrain
Fig. 27 Transmission Control Module Location
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DESCRIPTION AND OPERATION (Continued)
CVIs by monitoring how long it takes for a gear
change to occur (Fig. 28).
Gear ratios can be determined by using the DRB
Scan Tool and reading the Input/Output Speed Sen-
sor values in the “Monitors” display. Gear ratio can
be obtained by dividing the Input Speed Sensor value
by the Output Speed Sensor value.
For example, if the input shaft is rotating at 1000
rpm and the output shaft is rotating at 500 rpm,
then the TCM can determine that the gear ratio is
2:1. In direct drive (3rd gear), the gear ratio changes
to 1:1. The gear ratio changes as clutches are applied
and released. By monitoring the length of time it
takes for the gear ratio to change following a shift
request, the TCM can determine the volume of fluid
used to apply or release a friction element.
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.
Fig. 28 Example of CVI Calculation
1 – OUTPUT SPEED SENSOR
2 – OUTPUT SHAFT
3 – CLUTCH PACK
4 – SEPARATOR PLATE
5 – FRICTION DISCS
6 – INPUT SHAFT
7 – INPUT SPEED SENSOR
8 – PISTON AND SEAL
CLUTCH VOLUMES
Clutch
When Updated
Proper Clutch
Volume
L/R
2-1 or 3-1
downshift
45 to 134
2C
3-2 kickdown
shift
25 to 85
OD
2-3 upshift
30 to 100
4C
3-4 upshift
30 to 85
UD
4-3 kickdown
shift
30 to 100
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DESCRIPTION AND OPERATION (Continued)
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
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. 29). 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.
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DESCRIPTION AND OPERATION (Continued)
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