Torque Converter Clutch: Testing and Inspection
***This has been updated by TSB # 896E7, dated Mar '89.
Chart C-8A - Torque Converter Clutch (TCC) (Part 1 of 2):
Chart C-8A Electrical Circuit:
CHART C-8A TORQUE CONVERTER CLUTCH (TCC)
Circuit Description:
The purpose of the automatic transmission [1][2]torque converter clutch feature is to eliminate the power loss of the torque converter stage 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 [1][2]torque converter clutch is applied which results in straight through mechanical coupling from the engine to transmission. When the transmission solenoid is deactivated, the torque converter clutch 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 3rd and 4th gears.
TCC will engage when:
Engine warmed up
Vehicle speed above a calibrated value (about 28 mph 45 km/h)
Throttle position sensor output not changing, indicating a steady road speed
Brake switch closed
Test Description: Numbers below refer to circled numbers 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 B+ to terminal "A".
4. This test confirms that the ECM has the ability to turn the TCC "ON".
Diagnostic Aids:
The "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 "Scan" indicates the TCC driver has turned "ON."
CHART C-8A TORQUE CONVERTER CLUTCH (TCC)
Chart C-8A - Torque Converter Clutch (TCC) (Part 2 of 2):
CHART C-8A TORQUE CONVERTER CLUTCH (TCC)
Circuit Description:
The 3rd gear switch in this vehicle is open in 3rd and 4th gear. The ECM uses this signal to disengage the TCC when going into a downshift.
The fourth gear switch is open in fourth gear.
Test Description: Numbers below refer to circled numbers 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 3rd or 4th gear switch.
2. Determines whether the switch or signal circuits 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(es) should be grounded in this step, disconnecting the TCC connector should cause the "Scan" switch state to change.
4. The switch state should change when the vehicle shifts into 3rd gear.
Diagnostic Aids:
If vehicle is road tested because of a TCC related problem, be sure the switch states do not change while in 4th gear because the TCC will disengage. If switches change state, carefully check wire routing and connections.