Camaro Z28 V8-305 5.0L VIN F FI (1991)
Wiring Diagram Torque Converter Clutch
CIRCUIT DESCRIPTION:
A fourth gear switch (mounted in the transmission) 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. Temperature switch is normally open. Transmission must be in 4th gear, for the temperature
switch to apply TCC to cool the transmission fluid. Temperature switch lock at 155~C +/- 3.8~C and unlock at 143~C +/- 5~C.
TEST DESCRIPTION:Numbers below refer to circled numbers on the diagnostic chart.
1.
Unless the switch or CKT 446 is stuck closed or circuit 446 is shorted to ground. The "Scan" should display "NO," indicating the trans. is not in
4th gear. The 4th gear switch should only be open while in 4th gear.
2.
Checks the operation of the 4th gear switch. When the trans. shifts into 4th gear the switch should open and the "Scan" should display "YES."
3.
Disconnecting the TCC connector simulates an open switch to determine if CKT 446 is shorted to ground or the problem is in the transmission.
4.
This step determines if the ECM and wiring are OK. Grounding CKT 446 should cause the "Scan" to display "NO," indicating the trans. is not in
4th gear.
DIAGNOSTIC AIDS:
A road test may be necessary to verify the customer complaint. If the "Scan" indicates TCC is turning "ON" and "OFF" erratically, check the state of the
4th gear switch to be sure it is not changing states under a steady throttle position. If the switch is changing states, check connections and wire routing
carefully. Also if the 4th gear switch is always open the TCC may engage as soon as sufficient oil pressure is reached.
Part 3 of 3
