Chrysler PT Cruiser 2001 Service Manual Supplement page 1249

21 - 64 TRANSAXLE
DESCRIPTION AND OPERATION (Continued)
TRANSMISSION CONTROL MODULE
DESCRIPTION
The Transmission Control Module (TCM) is located
behind the left fender and is fastened to the left
frame rail forward of the suspension (Fig. 13). It
mounts on a bracket that is fastened to the rail.
Fig. 13 Transmission Control Module (TCM)
1 – BRACKET
2 – LEFT RAIL
3 – TRANSMISSION CONTROL MODULE (TCM)
OPERATION
The TCM is the controlling unit for all electronic
operations of the transaxle. The TCM receives infor-
mation regarding vehicle operation from both direct
and indirect inputs, and selects the operational mode
of the transaxle. Direct inputs are hardwired to, and
used specifically by the TCM. Indirect inputs origi-
nate from other components/modules, and are shared
with the TCM via the 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 (CKP)
• Transmission Range Sensor (TRS)
• Pressure Switches (L/R, 2/4, OD)
• Transmission Temperature Sensor (Integral to
TRS)
• Input Shaft Speed Sensor
• Output Shaft Speed Sensor
Location
Some examples of indirect inputs to the TCM
are:
• Engine/Body Identification
• Manifold Pressure
• Target Idle
• Torque Reduction Confirmation
• Speed Control ON/OFF Switch
• Engine Coolant Temperature
• Ambient/Battery Temperature
• Brake Switch Status
• DRB 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 (LR/CC, 2/4, OD and UD)
• Vehicle Speed (to PCM)
• Torque Reduction Request (to PCM)
An example of a TCM indirect outputs is:
• Transmission Temperature (to PCM)
In addition to monitoring inputs and controlling
outputs, the TCM has other important responsibili-
ties and functions:
• Storing and maintaining Clutch Volume Indices
(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 AND Pinion Factor procedures must be per-
formed. Refer to Service Procedures for proper pro-
cedures.
CLUTCH VOLUME INDEX (CVI)
An important function of the TCM is to monitor
Clutch Volume Index (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 transaxle gear ratio. This is important to the
CVI calculation because the TCM determines CVIs
by monitoring how long it takes for a gear change to
occur (Fig. 14).
PT