Firebird V8-305 5.0L VIN F FI (1987)
Wiring Diagram for Torque Converter Clutch
CHART C-8A TORQUE CONVERTER CLUTCH (TCC) DIAGNOSIS
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. The heart of the system
is a solenoid located inside the automatic transmission which is controlled by the ECM.
When the solenoid coil is activated ("ON") the torque converter clutch is applied which results in straight through mechanical coupling from the engine
to transmission. When the transmission solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the
conventional manner (fluid coupling between engine and transmission).
The ECM turns "ON" the TCC when coolant temperature is above 65 degrees C (149 degrees F), TPS not changing, and vehicle speed above a specified
value.
A 4th gear switch (mounted in the transmision) opens when the transmission shifts into 4th gear, and this switch is used by the ECM to modify TCC lock
and unlock points, when in a 4-3 downshift maneuver.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
1.
When a test light is connected from ALDL terminal "F" to ground, a test light "ON" indicates battery voltage is OK and the TCC solenoid is
disengaged.
2.
When the diagnostic terminal is grounded, the ECM should energize the TCC solenoid and the test light should go out.
Diagnostic Aids:
A "Scan" tool only indicates when the ECM has turned "ON" the TCC driver (grounded CKT 422) but 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." To determine if
the 4th gear switch is functioning properly, perform the checks in CHART C-8A (Part 2 of 2). The switches will not prevent TCC from functioning but
will affect TCC lock and unlock points. If the 4th gear switch circuit is always open the TCC may engage as soon as sufficient oil pressure is reached.
