Chart C-8A Torque Converter Clutch (TCC) Functional Check

Chart C-8A:

TCC Wiring Schematic:

CIRCUIT DESCRIPTION
The purpose of the Torque Converter Clutch (TCC) 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 are two solenoids located inside the transaxle which is controlled by the Powertrain Control Module (PCM).

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

The TCC Pulse Width Modulated (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.
^ Vehicle is in 3rd or 4th gear.
^ Vehicle is operating in "Hot Mode," which will cause the TCC to be engaged in 2nd gear.
^ "Hot Mode" will be in effect when transaxle temperature exceeds 130°C (266°F).

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

1. Ensures that the transaxle test box J 38791 is working properly, ignition power is being supplied to the transaxle solenoids, and CKTs 422 and 418 are not grounded.
2. Ensures that the PCM can control the TCC apply solenoid CKT 422 properly.
3. Ensures that the PCM can control the TCC PWM solenoid CKT 418.
4. Do not measure resistance until the ignition has been "OFF" for at least 10 seconds to ensure that the PCM has powered down completely.

DIAGNOSTIC AIDS
The Tech 1 only indicates when the PCM has commanded "ON" the TCC driver; 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 Tech 1 indicates the TCC driver has turned "ON." If functional check is performed and that all circuits are OK, refer to Automatic Transmissions for hydraulic and mechanical diagnosis.