POWER
TRAIN
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Automatic Transaxle
2-95
Normal Shutdown Routine
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When the ignition switch is turned off (column lock,
key out position), the TCM will go through a specific
shutdown routine.
For the first twenty minutes after ignition off, the
CPU remains in the “awake” mode. In tills off-time
tracking mode, the TCM continues to perform certain
functions such as predicting fluid temperature cal-
culations.
Longer off-time tracking is currently prohibited due
to battery drain concerns since the CPU remains
powered up during this time.
After 20 minutes have elapsed, the CPU will switch
into a Sleep mode. In this mode the TCM does
not perform any functions and its Keep Alive Memory
uses only a very small amount of current.
The TCM uses a “Keep Alive Memory” that must
always remain connected to the battery voltage
sup-
Fail-Safe Routine
The TCM is designed and programmed with what
is called a fail-safe routine. This routine constantly
monitors and checks all input and control features
for normal operation. The TCM uses inputs from
the PCM, transmission range and park neutral
switches, input and output speed signals, throttle
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position, ignition and pressure switches to determine
the desired outputs. The primary outputs are to
the four solenoid valves which control the transaxle
clutches. Changes in these solenoid outputs can
When a failure has been identified which prevents
continued safe transaxle operation, the TCM eventu-
ally goes into limp-in by turning off all of the sole-
noids. This provides for shift lever controlled opera-
tion of SECOND GEAR, NEUTRAL, REVERSE,
and PARK. The TCM has logic to ensure the limp-in
results in an ORDERLY SHUTDOWN. Certain fail-
ures will prevent an orderly shutdown, and an IM-
MEDIATE SHUTDOWN will occur.
Orderly Shutdown -A Shutdown routine is activated
with certain failures prior to opening the transmission
control relay. The result of an orderly shutdown is
dependent on the operating condition at the time
of the failure. If the transaxle is in Park, Reverse,
Neutral, or Second Gear, there is no additional action
needed by the TCM. The transmission control relay
is opened immediately because the power off state
of the transaxle has already been achieved.
If the transaxle is in first gear, then the shutdown
sequence (default to second gear) begins immedi-
ately.
If the transaxle is in third or fourth Gear above 45
b
mph, then the current gear range is maintained
to prevent the possibility of causing high engine
rpm and/or
engine braking.
ply. If the TCM is disconnected, the “Keep Alive
Memory” will be lost. This memory is where
d/agnos-
tic trouble codes and other learned values are
stored. These values may be clutch apply and re-
lease rates and clutch fill volumes. If the TCM is
disconnected from its direct battery voltage supply,
initial stored values are substituted for the erased
learned values when the CPU is re-initialized. These
values will then be updated as new values are
learned when operating the transaxle.
A code 12 will also be stored on any initialization
following a direct battery feed disconnection. Code
12 lets you know that a direct battery disconnection
has occurred.
result in changes in clutch pressures, pressure
switch states and input speeds. These changes
become the new input. If they are not as desired,
then the solenoid output is adjusted accordingly.
This feed-back control is referred to as a closed
loop system and is an integral part of fail-safe.
NOTE
The purpose of this section is to cover fail-safe
logic. Refer to the Fault Code Explanation section
for diagnostic information and probable causes.
The actual shutdown sequence to second Gear be-
gins once the vehicle speed drops below 45 mph.
The exception to this rule is when the vehicle is
at high speed and develops a solenoid circuit error.
If this occurs, a temporary “neutral” state is gener-
ated by venting all clutches to avoid incorrect clutch
combinations
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see Codes 41 to 44.
The shutdown sequence reduces the possibility of
having engine flare-up or clutch overlap (three
clutches applied) as the transaxle defaults to second
gear. This is accomplished by releasing the non
second gear clutches slightly before the transmis-
sion control relay is opened. This will occur when
the throttle angle is less than approximately
l/3
full open. At greater throttle angles, the transmission
control relay is immediately opened. This is done
because second gear clutches typically apply faster
than the non second gear clutches. Again, the pur-
pose for this sequence of events is to prevent more
than the correct number of clutches from being ap-
plied at the same time during moderate throttle
angles and to prevent engine flare at higher throttle
openings.
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