Chart C-8 Torque Converter Clutch (TCC) Diagnosis

Chart C-8A:

Transmission Control Wiring:

CIRCUIT DESCRIPTION
The purpose of the 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 and the fuel economy of a manual transaxle. The heart of the system is the TCC apply solenoid and the TCC PWM solenoid located inside the transaxle which is controlled by the PCM.

When the solenoid coil is activated ("ON,") the torque converter clutch is applied which results in straight through mechanical coupling from the engine to the wheels. When the transaxle (TCC) solenoid is deactivated ("OFF"), the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluid coupling between engine and transaxle).

The PWM solenoid varies the hydraulic pressure to make locking and unlocking of TCC smoother.

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. Determines whether fault is caused by a faulty solenoid or control circuit.

2. Checks availability of B+ on CKT 420.

3. Checks the PCM's ability to pulse the PWM solenoid "ON" and "OFF".

4. Electrical circuits have checked out. If there is a TCC engagement problem, it would be an internal transmission problem.

DIAGNOSTIC AIDS:
The "Scan" tool only indicates when the PCM has turned "ON" the TCC driver and this does not confirm that the TCC has engaged. To determine if TCC is functioning properly, road test the vehicle. Engine rpm should decrease when the "Scan" indicates the TCC driver has turned "ON."