EXPERTEC TSB (416510)

SERVICE MANUAL REFERENCE PAGES

• 6E3-C8-1 TCC SYSTEM
• 6E3-C8-6 CHART C-8A
• 6E3-C8-7 CHART C-8A
• 6E3-C8-8 CHART C-8A
• 6E3-C8-9 CHART C-8A

Fig 1: SECTION C8 - TORQUE CONVERTER CLUTCH (TCC) SYSTEM

PURPOSE

The 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 transmission through the torque converter. This reduces the slippage losses in the converter, which increases fuel economy.

OPERATION

For the converter clutch to apply, several conditions must be met:

• Internal transmission fluid pressure must be correct. For information on internal transmission operation, see SECTION 7A. This section will cover only the electrical operation of the TCC system.
• The ECM grounds a switch internally to turn "ON" a solenoid in the transmission. 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 (CTS). Engine must be warmed up before clutch can apply.
• Engine must be in "Closed Loop" operation.
• The 3T40 with torque management uses 2nd and 3rd gear switch inputs to the ECM. The ECM uses the switch signals for TCC engage and disengage points.
• The 4T60 with torque management uses 2nci, 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 volts supply to the TCC solenoid when the brake is depressed.

RESULTS OF INCORRECT OPERATION

The Torque 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 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 TPS to maintain cruising speed. The Owner's Manual section on TCC operation should be reviewed with the driver.

DIAGNOSIS

The diagnosis of the TCC system is covered in CHART C-8B. The facing page also contains diagnostic aids for using a Tech 1 "Scan" tool for diagnosing the TCC circuit.

CIRCUIT DESCRIPTION

The purpose of the automatic transmission torque converter clutch feature is to eliminate the power loss of the torque converter when the vehicle is in a cruise condition. This allows the convenience of the automatic transmission and the fuel economy of a manual transmission. The heart of the system is a solenoid located inside the automatic transmission which is controlled by the ECM.

When the solenoid coil is activated ("ON"), the Torque Converter Clutch (TCC) is applied which results in straight through mechanical coupling from the engine to transmission. When the transmission solenoid is deactivated, the Torque Converter Clutch (TCC) is released, which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission).

The TCC will engage on a warm engine under given road load in 2nd and 3rd gears. TC C will engage when:

• Brake switch closed.
• Coolant temperature is above 65 degrees Celsius (149 degrees Fahrenheit).
• Engine "Closed Loop" condition.
• Vehicle speed above a calibrated value (37 mph 59 km/h - 45 mph 71 km/h).
• Throttle position not changing, indicating a steady speed.

TEST DESCRIPTION

Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test checks the functional operation of the TCC circuit.
2. This test checks the TCC control driver in the ECM.
3. This test will confirm that there is BATT to terminal "A".
4. This test confirms that the ECM has the ability to turn the TCC "ON."

DIAGNOSTIC AIDS

A Tech 1 "Scan" tool only indicates when the ECM has turned "ON" the TCC driver, and this does not confirm that the TCC has engaged. To determine if TCC is functioning properly, engine RPM should decrease when the Tech 1 "Scan" tool indicates the TCC driver has turned "ON." A thermostat that is stuck open or opens at too low a temperature may result in an inoperative TCC.

CIRCUIT DESCRIPTION

The 2nd gear signal switch in this vehicle should be open in 2nd and 3rd gear. The ECM uses this 2nd gear signal to disengage the TCC when going into a downshift.

The 3rd gear switch should be open in 3rd gear.

TEST DESCRIPTION

Number(s) below refer to circled number(s) on the diagnostic chart.

1. Some "Scan" tools display the state of these switches in different ways. Be familiar with the type of tool being used. Since both switches should be in the closed state during this test, the tool should read the same for either the 2nd or 3rd gear switch.
2. Determines whether the switch or signal circuit is open. The circuit can be checked for an open by measuring the voltage (with a voltmeter) at the TCC connector (should be about 12 volts).
3. Because the switch(s) should be grounded in this step, disconnecting the TCC connector should cause the Tech 1 "Scan" tool switch state to change.
4. The switch state should change when the vehicle shifts into 2nd gear.

DIAGNOSTIC AIDS

If vehicle is road tested because of a TCC related problem, be sure the switch states do not change while in 3rd gear because the TCC will disengage.

If switches change state, carefully check wire routing and connections.