Part 2 of 2

Chart C-8A Part 2 Of 2:

Wiring Diagram:

CIRCUIT DESCRIPTION:

A fourth gear switch (mounted in the transmission) is normally open and closes when the transmission shifts into 4th gear. This switch is used by 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 4th gear for the temperature switch to apply TCC to cool transmission fluid. Temperature switch locks between approximately 136~C (277~F) and 126~C (258~F).


CIRCUIT DESCRIPTION:



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 transmission is not in 4th gear. The 4th gear switch should only be closed while in 4th gear.

2. This step checks the operation of the 4th gear switch. When the transmission shifts into 4th gear the switch should close 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 circuit 446 should cause the scan to display yes, indicating the transmission is 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.