Chart C-8 Torque Converter Clutch (TCC) Diagnosis

Torque Converter Clutch Circuit:

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. The TCC will engage at approx. 25 mph on vehicles equipped with the front and rear A/C option. Vehicles equipped with the front only A/C option will allow TCC engagement at 2 different speeds. If A/C is selected "ON" the TCC engages at approximately 35 mph. When A/C is selected "OFF" the TCC engages at approximately 25 mph. This difference is due to the use of the VS non cycling compressor used in front only A/C equipped vehicles. The A/C control relay driver is connected to the TCC selector at the ECM allowing for a smooth engagement of the TCC when an A/C load is present.

Fused battery ignition is supplied to the TCC solenoid through the brake switch, and the third gear apply switch. The ECM will engage TCC by grounding CKT 422 to energize the solenoid.

TCC will engage when:
^ Engine warmed up.
^ Vehicle speed above a calibrated value (about 32 mph 51 km/h).
^ Throttle Position Sensor (TPS) output not changing, indicating a steady road speed.
^ Third gear switch closed.
^ Brake switch closed.

Torque Converter Clutch Diagnostic Chart:

Test Description
Number(s) below refer to circled number(s) 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 Tech 1 "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 Tech 1 "Scan" tool indicates the TCC driver has turned "ON."