SENSORS
There are three pressure switches which identify
solenoid application. The pressure switches are incor-
porated in an assembly with the solenoids. Two speed
sensors read input (torque converter turbine) and
output (parking sprag) speeds. There is also a Trans-
mission Range Sensor (TRS) which senses manual
valve position.
Engine speed, throttle position, temperature, etc., are
also observed. Some of these signals are read directly
from the engine control sensors; others are read from a
multiplex circuit with the engine controller.
ADAPTIVE CONTROLS
These controls function by reading the input and
output speeds over 140 times a second and respond-
ing to each new reading. This provides the friction
element control needed to make smooth clutch-to-
clutch shifts for all gear changes without the use of
overrunning clutches. As with most automatic tran-
saxles, all shifts involve releasing one element and
applying a different element. In simplified terms, the
upshift logic allows the releasing element to slip
backwards slightly to ensure that it does not have
excess capacity; the apply element is filled until it
begins to make the speed change to the higher gear;
its apply pressure is then controlled to maintain the
desired rate of speed change until the shift is com-
plete. The key to providing excellent shift quality is
precision; for example, as mentioned, the release ele-
ment for upshifts is allowed to slip backwards
slightly; the amount of that slip is typically less than
a total of 20 degrees. To achieve that precision, the
transmission control module learns the characteris-
tics of the particular transaxle that it is controlling.
It learns:
• The release rate of the releasing element.
• The apply time of the applying element.
• The rate the apply element builds pressure.
This method achieves more precision than would be
possible with exacting tolerances. It can also adapt to
any changes that occur with age or environment.
For kickdown shifts, the control logic allows the
releasing element to slip. Then controls the rate at
which the input (and engine) accelerate. When the
lower gear speed is achieved, the releasing element
reapplies to maintain that speed until the apply ele-
ment is filled. This provides quick response and a
smooth torque exchange since the release element
can control the rate of torque increase. This control
can make any powertrain feel more responsive with-
out increasing harshness.
Adaptive controls respond to input speed changes.
They compensate for changes in engine or friction
element torque. Thus providing consistent shift qual-
ity for the life of the transaxle.
DIAGNOSTICS
These
controls
also
provide
comprehensive,
on-board
transaxle
diagnostics.
The
information
available can aid in transaxle diagnosis. For exam-
ple, apply element buildup rate indicates solenoid
performance. Also included are self-diagnostic func-
tions which allow the technician to test the electronic
controls. The transmission control module monitors
its critical functions, records any malfunctions, and
the number of engine starts since the last malfunc-
tion. The technician can use this information in the
event of a customer complaint. Refer to the 42LE
Transaxle Diagnostic Procedure Manual for specifics.
TRANSMISSION CONTROL MODULE
The transmission control module is located in the
engine compartment between the left front fender
and the battery. It is held in place by four mounting
screws. The battery must be moved to gain access to
the transmission control module.
NOTE: If the transmission control module has been
replaced, refer to Quick Learn Procedure. This pro-
gram will allow the transmission control module to
learn the characteristics of the vehicle.
TRANSMISSION CONTROL RELAY
The transmission control module controls power to
the solenoid pack through the transmission control
relay. The relay is located in the power distribution
center on the left side of the engine compartment.
Refer to the 42LE Transaxle Diagnostic Procedures
Manual for test procedures.
SOLENOID ASSEMBLY
The transaxle solenoid pack is located on the top
side of the valve body. The valve body must be
removed from the transaxle in order to service the
solenoid pack.
The solenoid pack contains four solenoids. If any
one of the solenoids fail, all of the solenoids must be
replaced. There are no serviceable parts for the sole-
noid pack.
Refer to the 42LE Transaxle Diagnostic Procedures
Manual for diagnostic test procedures.
SHIFTER/IGNITION INTERLOCK
The ignition interlock system connects the auto-
matic transmission shifter and the lock system. With
the ignition key in the LOCK or ACCESSORY posi-
tion, the interlock system holds the transmission
shifter in park. When the key is in the OFF or RUN
position the shifter unlocks and can be moved to any
position. Also, if the shifter is not in PARK, the sys-
tem prevents the operator from turning the ignition
switch to the LOCK or ACCESSORY positions.
300M
TRANSAXLE
21 - 5
DESCRIPTION AND OPERATION (Continued)