Transmission Control System

PURPOSE
The Torque Converter Clutch (TCC) system uses two Powertrain Control Module (PCM) controlled solenoids for engagement; a Pulse Width Modulated (PWM) solenoid valve, and an apply solenoid valve in the automatic transaxle to couple the engine flywheel to the output shaft of the transaxle through the torque converter. This reduces the slippage losses in the converter, increasing fuel economy.

OPERATION
For the torque converter clutch to apply two conditions must he met:

^ Internal transaxle fluid pressure must be correct.
^ The PCM grounds switches internally to turn "ON" solenoids in the transaxle. This moves check balls, which will allow the torque converter clutch to apply, if the hydraulic pressure is correct. The TCC "APPLY" solenoid controls the flow of transmission fluid to the TCC. The TCC Pulse Width Modulated (PWM) solenoid varies the hydraulic pressure at the converter clutch regulator valve to make locking and unlocking of TCC smoother.

The PCM controls the TCC apply and PWM solenoids after looking at several parameters:

^ Vehicle Speed Sensor (VSS). Speed must be above a certain value before the clutch can apply.
^ Engine Coolant Temperature (ECT) sensor. Engine must he warmed up before clutch can apply.
^ Throttle Position (TP) sensor. After the converter clutch applies, the PCM uses the information from the TP sensor to release the clutch when the vehicle is accelerating or decelerating at a certain Tate.
^ The TCC brake switch, which opens a 12 volt signal to the PCM when the brake pedal is depressed.

RESULTS OF INCORRECT OPERATION
If the torque converter clutch does not apply, fuel economy may be lower than expected. If the vehicle speed sensor fails, the TCC will not apply.

The Torque Converter Clutch (TCC) system has different operating characteristics than an automatic transaxle without TCC. If the driver complains of a "chuggle" or "surge" condition, the vehicle should be road tested and compared to a similar vehicle 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 throttle position to maintain cruising speed. The owner's manual section on TCC operation should be reviewed with the driver.

If the TCC PWM solenoid is stuck open, TCC may engage harshly.

The Tech 1 displays the PWM control as a duty cycle. 0% duty cycle is equal to 0 pressure/no TCC. 100% duty cycle is equal to full line pressure/TCC locked.