Part 2 of 2

Chart C-8 Part 2 Of 2:

Chart C-8 Wiring Diagram:

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.

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

1. Unless the switch or CKT 446 is open "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. 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.