Torque Converter Clutch Solenoid: Description and Operation

Torque Converter Clutch (TCC) Solenoid:

PURPOSE
The [1][2]Torque Converter Clutch (TCC) system uses a solenoid operated valve in the automatic transmission to couple the engine flywheel to the output shaft of the transaxle through 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 transaxle fluid pressure must be correct. For information on internal transaxle/transmission operation, see TESTING and INSPECTION. 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 transaxle. 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.
- The 4T60 transaxle uses 3rd and 4th gear switches which are direct inputs to the ECM. The ECM uses the switch signals for TCC engage and disengage points.
- 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 3T40 transaxles, a third gear switch (normally open) is placed in series on the battery side of the TCC solenoid. This switch prevents TCC application until the transaxle is in third gear. Then the switch closes, completing the circuit to the ECM.
- Refer to chart C-8a for further diagnosis. Testing and Inspection

RESULTS OF INCORRECT OPERATION
If the converter clutch does not apply, fuel economy may be lower than expected. If the vehicle speed sensor fails, the [1][2]Torque Converter Clutch (TCC) will not apply. If the 3rd gear switch does not operate, the TCC will not apply at the right time.

The TCC system has different operating characteristics than an automatic transaxle 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, due to the change in Throttle Position Sensor (TPS) to maintain cruising speed. The owner's manual section on TCC operation should be reviewed with the driver.