TRANSMISSION CONTROL
MODULE
DESCRIPTION
The transmission control module (TCM) receives,
processes and sends various digital and analog sig-
nals related to the automatic transmission. In addi-
tion, it processes information received from other
vehicle systems, such as engine torque and speed,
accelerator pedal position, wheel speed, kick-down
switch, traction control information, etc.
The TCM is located under the driver’s seat and is
connected to other control modules via a CAN bus. It
controls all shift functions to achieve smooth shift
comfort in all driving situations considering:
• Vehicle speed.
• Transmission status.
• Position of selector lever.
• Selected shift range.
• CAN signals.
• Engine Status.
Engine speed limits may be reached in all gears
with full throttle or in kick-down operation. In for-
ward driving, the shift range of the forward gears
can be adjusted by the operator by tipping the selec-
tor lever to the left or right (AutoStick). However, the
TCM features a downshift inhibitor to prevent the
engine from overspeeding.
OPERATION
The transmission control module (TCM) deter-
mines the current operating conditions of the vehicle
and controls the shifting process for shift comfort and
driving situations. It receives this operating data
from sensors and broadcast messages from other
modules.
The TCM uses inputs from several sensors that are
directly hardwired to the controller and it uses sev-
eral indirect inputs that are used to control shifts.
This information is used to actuate the proper sole-
noids in the valve body to achieve the desired gear.
The shift lever assembly (SLA) has several items
that are monitored by the TCM to calculate shift
lever position. The reverse light switch, an integral
part of the SLA, controls the reverse light relay con-
trol circuit. The Brake/Transmission Shift Interlock
(BTSI) solenoid and the park lockout solenoid (also
part of the SLA) are controlled by the TCM.
The ECM and ABS broadcast messages over the
controller area network (CAN C) bus for use by the
TCM. The TCM uses this information, with other
inputs, to determine the transmission operating con-
ditions.
The TCM:
• determines the momentary operating conditions
of the vehicle.
• controls all shift processes.
• considers shift comfort and the driving situation.
The TCM controls the solenoid valves for modulat-
ing shift pressures and gear changes. Relative to the
torque being transmitted, the required pressures are
calculated from load conditions, engine rpm, vehicle
speed, and ATF temperature.
The following functions are contained in the TCM:
• Shift Program
• Downshift Safety
• Torque Converter Lock-Up Clutch.
• Adaptation.
This transmission does not have a TCM relay.
Power is supplied to the SLA and the TCM directly
from the ignition.
Fig. 3 ECM
1 - BRACKET
2 - ECM
3 - BRACKET TENSIONING SPRINGS
VA ELECTRONIC CONTROL MODULES 8E - 5
ENGINE CONTROL MODULE (Continued)
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