Transmission Converter Clutch (Tcc); Description; Diagnosis; On-Vehicle Service - GMC G Service Manual

6E2-54 DIESEL EMISSIONS

TRANSMISSION CONVERTER CLUTCH (TCC)

DESCRIPTION

TCC SYSTEM
The Transmission Converter Clutch (TCC) System uses
a solenoid operated valve, in the automatic transmission, to
couple the engine flywheel to the output shaft of the trans­
mission through the torque 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,
refer to AUTOMATIC TRANSMISSION (SEC. 7A).
This section will cover only the electrical operation of
TCC system.
• The ECM completes a ground circuit, to energize a
TCC apply solenoid in the transmission, which moves
a check ball in a fluid line (Figure 32). This allows the
converter clutch to apply, if the hydraulic pressure is
correct, as described above.
P H TCC SOLENOID
i 2 | CHECK B A LL
Figure 32 — TCC Solenoid
3 J CHECK B A L L SEAT
4S 0548-6E
• Throttle Position Sensor (TPS) - After the converter
clutch applies, the ECM uses the information from the
TPS to release the clutch, when the vehicle is accel­
erating, or decelerating, at a certain rate.
• Brake Switch - This switch, in the TCC circuit, opens
when the brake pedal is depressed. This de-ener­
gizes the TCC solenoid.

DIAGNOSIS

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 Convert Clutch (TCC) system has dif­
ferent operation characteristics than an automatic transmis­
sion without TCC. If the driver complains of a "chuggle" or a
"surge" condition, the vehicle should be road tested and
compared to a similar vehicle, to see if a real problem
exists. The Owner's Manual section on TCC operation
should be reviewed with the driver. Another TCC complain
may be a downshift felt, when going up a grade, especially
with cruise control. This may not be a downshift, but a
clutch disengagement due to the change in TPS to maintain
cruising speed.
The electrical diagnosis of the TCC system is covered in
the appropriate "Transmission Converter Clutch Electrical
Diagnosis" chart.
If the ECM detects a problem in the VSS system, a Code
24 should set. In this case, refer to Code 24 chart.

ON-VEHICLE SERVICE

• Refer to AUTOMATIC TRANSMISSION (SEC. 7A)
for TCC solenoid replacement.
• Refer to INSTRUMENT PANEL AND GAGES (SEC.
8C) for brake switch replacement.
• Refer to Diesel Electronic Control system for repair of
wiring and replacement of the ECM.