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Wiring Diagram For TCC:

CIRCUIT DESCRIPTION:

A fourth gear switch (mounted in the transmission) opens when the transmission shifts into fourth gear. This switch is used by the ECM to modify TCC lock and unlock points when in a 4-3 downshift maneuver. The temperature switch is normally open. The transmission must be in fourth gear for the temperature switch to close and apply TCC to cool the transmission fluid. The temperature switch closes at 137°C +/- 3.5°C (279°F +/- 7°F) and opens at 126°C +/- 5°C (259°F +/- 9°F).


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

1. Unless the switch is stuck closed or circuit 446 is shorted to ground, the "Scan" tool should display "NO," which indicates that the transmission is not in fourth gear. The fourth gear switch should only be closed in fourth gear.

2. This checks the operation of the fourth gear switch. When the transmission shifts into fourth gear, the switch should close and the "Scan" tool should display "YES."

3. Disconnecting the TCC connector simulates an open switch to determine if circuit 446 is shorted to ground, or the problem is in the transmission.

4. This step determines if the ECM and wiring are OK. Grounding circuit 446 should cause the "Scan" tool to display "YES," which indicates the transmission is in fourth gear.


DIAGNOSTIC AIDS:

A road test may be necessary to verify the customer complaint. If the "Scan" tool indicates that TCC is turning "ON" and "OFF" erratically, check the state of the fourth 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. If the fourth gear switch is always open, the TCC may engage as soon as sufficient oil pressure is reached.