Reference Manual

---

Chapter 2: Transmissions: Torque Converter Clutch Operation

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/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 meet:

• Internal transmission / transaxle fluid pressure must be correct.
• The ECM grounds the TCC solenoid in the transmission which moves a check ball in a fluid line. This 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:

• Vechicle 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.
• Gear Select Switch. Some transmissions use a 3rd or 4th gear switch to send a signal to the ECM telling it what gear the transmission / transaxle is in. The ECM uses this information to vary the conditions under which the clutch applies or releases. However, the transmissions / transaxles does not have to be in high gear in order for the ECM to turn the clutch on. Transmissions / transaxles using gear select switches can be identified by 3 or 4 wires coming out of the TCC connector.

On some transmissions/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 transmission/transaxle is in third gear and then the switch closes, completing the circuit to the ECM.

Also some transmissions/transaxles use a 4-3 pulse switch (or 3-2 on some 3 speed transmissions/transaxles), to open the TCC solenoid circuit momentarily during a downshift.

Results of Incorrect TCC Operation

If the converter clutch is applied at all times, the engine will stall immediately, just as in a manual tranmission/transaxle 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. If the 3rd or 4th gear switch does not operate, the TCC will not apply at the right time.

The Transmission/transaxle 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 not be a downshift, but a clutch disengagement due to the change in TPS to maintain cruising speed.