Pontiac Fiero 1988 Service Manual page 786

AUTOMATIC TRANSAXLE 125C-45
IVERTER CLUTCH (TCC)
TORQUE COF
DIAGNOSIS
To properly diagnose the Torque Converter
Clutch (TCC) system perform all electrical testing first
and then the hydraulic testing. Refer to Torque
Converter Section 6E2-C8 for additional information.
The TCC is applied by fluid pressure which is
controlled by a solenoid located inside the Automatic
Transaxle assembly. The solenoid is energized or
released by making or breaking an electrical circuit
thru a combination of switches and sensors.
TCC Electrical Diagnosis
• For electrical diagnosis of TCC, refer to the
specific vehicle section in Section 8A, Electrical
Diagnosis.
• For diagnosis of emission control related
components of TCC, refer to the specific section
of 6E, Driveability and Emissions.
B For the diagnosis of TCC Hydraulic Controls,
refer to the Procedure and Wiring Diagrams
provided in this section.
Functional Check Procedure
Inspect
1. Install a tachometer
2. Operate the vehicle until proper operating
temperature is reached
3. Drive vehicle at 50-55 mph (80-88 Km/h) with
light throttle (road load)
4. Maintaining throttle, lightly touch the brake
pedal and check for a slight bump when the TCC
releases and a slight increase in engine speed
(RPM).
5. Release the brake, slowly accelerate and check for
a re-apply of the converter clutch and a slight
decrease in engine speed (RPM).
Preliminary Checking Procedure
The purpose of the preliminary checking
procedure is to isolate external (electrical) problems
from internal (electrical or mechanical) ones.
Important
• Use only a scale type ohmmeter. High impedance
type ohmmeters and those with a digital readout
will not work.
• An ALCL scanner may be used to verify the
electrical circuit. Remember, a completed circuit
does not indicate that the solenoid will apply.
m Do not bench test using an automotive type
battery. Accidentally crossed wires will damage
the internal diodes of the TCC solenoid.
External Controls
Inspect
# Connect voltmeter between
connector and ground.
transmission
• Turn key "ON"
• If 0 or low voltage is found, refer to Sections 6E
and 8A for electrical diagnosis.
• If 12 volts are present at the connector, refer to
the TCC hydraulic diagnosis.
TORQUE CONVERTER EVALUATION
Torque Converter Stator
The Torque Converter Stator roller clutch can
have one of two different type malfunctions:
A . S t a t o r A s s e m b l y f r e e w h e e l s in b o t h
d i r e c t i o n s .
B„ S t a t o r A s s e m b l y r e m a i n s l o c k e d u p a t a l l
t i m e s .
Condition A-Poor Acceleration Low Speed
The car tends to have poor acceleration from a
standstill. At speeds above 30-35 mph (50-55 km/h),
the car may act normal. If poor acceleration is noted,
it should first be determined that the exhaust system
is not blocked, the engine timing is correct and the
transaxle is in first (1st) gear when starting out.
If the engine freely accelerates to high r.p.m. in
"NEUTRAL" (N), it can be assumed that the engine
and exhaust system are normal. Checking for poor
performance in "Drive'' and Reverse will help
determine if the stator is freewheeling at all times.
Condition B-Poor Acceleration High Speed
Engine r.p.m. and car speed limited or restricted
at high speeds. Performance when accelerating from a
standstill is normal. Engine may over-heat. Visual
examination of the converter may reveal a blue color
from over-heating.
If the converter has been removed, the stator
roller clutch can be checked by inserting a finger into
the splined inner race of the roller clutch and trying to
turn the race in both directions. The inner race should
turn freely clockwise, but not turn or be very difficult
to turn counterclockwise.
Do not use such items as the driven sprocket
support or shafts to turn the race, as the results may
be misleading.
The Converter Should be Replaced If:
• Leaks externally, such as at the hub weld area.
• Converter has an imbalance which cannot be
corrected. (Refer to Converter Vibration Test
Procedure).
• Converter is contaminated with engine coolant
containing antifreeze.
The Converter Should Not be Replaced If:
• The fluid has an odor, is discolored, and there is
no evidence of metal or clutch facing particles in
the fluid.
• The threads in one or more of the three converter
bolt holes are damaged.
Correct with thread insert. Refer to Section