Part 2 of 2

Chart C-8A, Part 2 of 2.:

Chart C-8A Wiring Diagram:

CIRCUIT DESCRIPTION:

The overdrive switch (mounted in in the console) is used to modify TCC engagement speeds. The TCC will engage on a warm engine, under a given load, in 2nd, 3rd and 4th gear at about 30 mph, if the gear selector is in overdrive. If 2nd or (D) drive range is selected, the overdrive switch should be closed and the ECM will not engage TCC until vehicle speed reaches about 40 mph. This switch will help eliminate the TCC from engaging and disengaging in city traffic.

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. With the gear switch in overdrive, the "Scan" should display "YES". In this position, TCC will engage at about 30 mph.

2. Circuit 925 can be checked for continuity by measuring for 12 volt signal from the ECM with a DVOM. If the 12 volts is present, the switch is mis-adjusted or faulty.

3. This step should cause the switch to close and the "SCAN" should display "NO."

4. Unless the switch or circuit 446 is open, the "SCAN" should display "NO", indicating the transmission is not in 4th gear. The 4th gear switch should only be open while in 4th gear.


5. This step will determine if the ECM and wiring are OK. Grounding circuit 446 should cause the "Scan" to display "NO", indicating the transmission is not in 4th gear.

6. Checks the operation of the 4th gear switch. When the transmission shifts into 4th gear, the switch should open and the "Scan should display "YES".

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

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.