Chart C-8A Torque Converter Clutch (TCC) Electrical Diagnosis

Flowchart C-8A - 3T40:

Chart C-8A Torque Converter Clutch (TCC)- 3T40:

CIRCUIT DESCRIPTION
The purpose of the torque converter clutch (TCC) feature is to eliminate the power loss of the torque converter stage when the vehicle is in a cruise condition. This allows for the convenience of the automatic transaxle and the fuel economy of a manual transaxle.
Fused battery ignition is supplied to the TCC solenoid through the brake switch, and the third gear apply switch. The Electronic Control Module (ECM) will engage TCC by grounding CKT 422 to energize the solenoid.

The TCC will engage when:
- Engine warmed up
- Vehicle speed above a calibrated value [about 51 km/h (32 mph)]
- Throttle position sensor (TPS) output not changing, indicating a steady road speed
- Third gear switch closed
- Brake switch closed

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

1. Light "OFF" confirms the third gear apply switch is open.
2. At 25 mph the transaxle/transmission third gear apply switch should close. Test light will come "ON" and confirm battery supply and closed brake switch.
3. Grounding the diagnostic terminal with ignition "ON," engine "OFF," should energize the TCC solenoid by grounding CKT 422. This test 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" will turn "ON" as CKT 422 is grounded.

DIAGNOSTIC AIDS
A "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."