Pontiac Fiero 1988 Service Manual page 698

D R I V E A B I L I T Y
A M P EMISSIONS - ' I' ^ , \ U ? C - ^ SE3-CS-1
SECTIOi
TRANSMISSION/TRANSAXLE
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AMD MANUAL TRAMS
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GENERAL DESCRIPTION . . C8-1
PURPOSE
C8-1
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Results of Incorrect Operation C8-1
DIAGNOSIS C8-2
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PARTS INFO^.V'AT CM!
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GENERAL DESCRIPTION
PURPOSE
The transmission/transaxle converter clutch
(TCC) System uses a solenoid operated valve in the
automatic transmission to couple the engine flywheel
to the output shaft of the transmission thru the torque
converter. This reduces the slippage losses in the
converter, which increases fuel economy.
OPERATION
For the converter clutch to apply, two conditions
must be met:
• Internal transmission fluid pressure must be
correct. For information on internal transmission
operation, see Section "7A". This section will cover
only the electrical operation of the TCC system.
• The electronic control module (ECM) grounds a
switch Internally to turn on a solenoid In the
transmission. This moves a check ball, which will
allow the converter clutch to apply, if the
hydraulic pressure is correct, as described above.
The ECM controls the TCC apply solenoid by
looking at several sensors:
• Vehicle Speed Sensor (VSS). Speed must be above
a certain value before the clutch can apply.
• Coolant Temperature Sensor. Engine must be
warmed up before clutch can apply.
• Throttle Position Sensor (TPS). After the
converter clutch applies, the ECM uses the
information from the TPS to release the clutch
when the car is accelerating or decelerating at a
certain rate.
• Another switch used in the TCC circuit is a brake
switch which opens the 12 volt supply to the TCC
solenoid when the brake is depressed.
• On 125C transmissions a third gear switch
(normally open) is placed in series on the battery
side of the TCC solenoid.
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application until the
transmission is in third gear. Then the switch closes,
completing the circuit to the ECM.
Results of I n e x a c t Operation
If the converter
clutch is applied at
all
times,
the
engine will stall immediately, just as in a manual
transmission with the clutch applied.
If the converter clutch does not apply, fuel
economy may be lower than expected. If the Vehicle
Speed Sensor fails, the TCC will not apply.
The transmission converter clutch (TCC) system
has different operating characteristics than an
automatic transmission without TCC. If the driver
complains of a "chuggle" or "surge" condition, the car
should be road tested and compared to a similar car to
see if a real problem exists. Another TCC complaint
may be a downshift felt when going up a grade,
especially with cruise control. This may be clutch
disengagement rather than a downshift, due to the
change in TPS to maintain cruising speed.