Torque Converter Clutch: Testing and Inspection

Chart C-8A:

Chart C-8A Wiring Diagram:

CIRCUIT DESCRIPTION:

The purpose of the automatic transmission 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.

Voltage is supplied to the TCC solenoid through the brake switch and transmission second gear apply switch. The ECM will engage the TCC by grounding CKT 422 to energize the solenoid.

The TCC will engage when:


^ Vehicle speed above a calibrated value (about 32 mph 51 km/h).
^ Engine warmed up.
^ Throttle position sensor output not changing, indicating a steady road speed.
^ Transmission third gear switch closed.
^ Brake switch closed.
^ TCC in-line apply switch closed.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Light "OFF" confirms that transaxle third gear apply switch is open.

2. At 25 mph, the transmission third gear switch should close. Test light will light and confirm battery supply, and closed brake switch.

3. Grounding the diagnostic terminal with the ignition "ON," engine "OFF," checks the ability of the ECM to supply a ground to the TCC solenoid. The test light connected from 12 volts to ALDL terminal "F" should turn "ON" as CKT 422 is grounded.

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, road test the vehicle. Engine rpm should decrease when the "Scan" indicates the TCC driver has turned "ON."