Diagnostic Aids
An engine coolant thermostat that is stuck open, or opens at too low a temperature, may result in an inoperative TCC. If TCC engages before "Scan" indicates, solenoid or sump overtemperature switch may be faulty.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Unless switch or circuit No. 446 is open, "Scan" tester should display "NO", indicating transmission is not in 4th gear. The 4th gear switch should only be open while in 4th gear.
- This test determines if the ECM and wiring are okay. Grounding circuit NO. 446 should cause "Scan" tester to display "NO", indicating the transmission is not in 4th gear.
- Checks operation of the 4th gear switch. When the transmission shifts into 4th gear the switch should open and "Scan" tester should display "YES".
- Disconnecting the TCC connector simulates an open switch to determine if circuit No. 446 is shorted to ground or the problem is in the transmission.
A road test may be necessary to verify the customer complaint. If the "Scan" tester indicates TCC is turning "ON" and "OFF" erratically, check the state of the 4th gear switch to be sure it is not changing state under a steady throttle position. If the switch is changing state, check connections and wire routing carefully. Also if 4th gear switch is always open, the TCC may engage as soon as sufficient oil pressure is reached.