Dodge Ram Truck 1500-2500-3500. Manual — part 317
MODULE-TRANSMISSION CONTROL
DESCRIPTION
The Transmission Control Module (TCM) (2) may be
sub-module within the Powertrain Control Module
(PCM) (3).
Or, for vehicles with a diesel engine, the Engine Con-
trol Module (ECM) (1). The PCM, and TCM when
equipped, is located at the right rear of the engine
compartment, near the right inner fender.
OPERATION
The Transmission Control Module (TCM) controls 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 are shared with the
TCM via the vehicle communication 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
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•
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
•
Scan Tool Communication
Based on the information received from these various 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
•
Torque Reduction Request
Some examples of TCM indirect outputs are:
•
Transmission Temperature (to PCM)
•
PRNDL Position (to cluster/CCN)
In addition to monitoring inputs and controlling outputs, the TCM has other important responsibilities and functions:
•
Storing and maintaining Clutch Volume Indexes (CVI)
•
Storing and selecting appropriate Shift Schedules
•
System self-diagnostics
•
Diagnostic capabilities (with scan tool)
NOTE: If the TCM has been replaced, the “Quick Learn Procedure” must be performed. (Refer to 8 - ELEC-
TRICAL/ELECTRONIC CONTROL MODULES/TRANSMISSION CONTROL MODULE - STANDARD PROCE-
DURE)
BATTERY FEED
A fused, direct battery feed to the TCM is used for continuous power. This battery voltage is necessary to retain
memory in the TCM. 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 Diagnostic Trouble Code (DTC) is set.
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CLUTCH VOLUME INDEXES (CVI)
An important function of the TCM is to monitor Clutch
Volume Indexes (CVI). CVIs represent the volume of
fluid needed to compress a clutch pack.
The TCM monitors gear ratio changes by monitoring
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 Output
Speed Sensor provides the TCM with output shaft
speed information.
By comparing the two inputs, the TCM can determine
transmission gear position. This is important to the
CVI calculation because the TCM determines CVIs by
monitoring how long it takes for a gear change to
occur.
Gear ratios can be determined by using the Scan Tool
and reading the Input/Output Speed Sensor 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 con-
trols. As friction material wears, the volume of fluid need to apply the element increases.
Certain mechanical problems within the input clutch assembly can cause inadequate or out-of-range element vol-
umes. Also, defective Input/Output Speed Sensors and wiring can cause these conditions. The following chart iden-
tifies the appropriate clutch volumes and when they are monitored/updated:
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
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 following:
•
Shift lever position
•
Throttle position
•
Engine load
•
Fluid temperature
•
Software level
As driving conditions change, the TCM appropriately adjusts the shift schedule. Refer to the following chart to deter-
mine the appropriate operation expected, depending on driving conditions.
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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 between 40° F and
80° F
- Normal operation (upshift,
kickdowns, and coastdowns)
- No EMCC
Hot
Oil temperature between 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
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