Diagnostic Aids

If vehicle is road tested because of a TCC related problem, ensure switch states do not change while in 4th gear. TCC will engage. If switches change state, carefully check wire routing and connections. If ECM, TCC solenoid and control circuitry are functioning correctly and TCC still does not apply properly, problem may be hydraulic or mechanical.

Each gear switch opens when appropriate clutch is applied. All gear switches are open in 4th gear.

1. Some scan tools display state of these switches in different ways. Be familiar with type of tool being used. All switches should be in closed state during this test and tool should read the same for 3rd and 4th gear switches.
2. This test determines whether switch of signal circuit is open. Circuit can be checked for an open by measuring voltage with a DVOM at TCC connector. Voltage should be about 12 volts.
3. Because switch(s) should be grounded in this step, disconnecting TCC connector should cause displayed switch states to change.
4. Switch state should change when vehicle shifts into 3rd gear.

If vehicle is road tested because of a TCC related problem, ensure switch states do not change while in 4th gear. TCC will engage. If switches change state, carefully check wire routing and connections. If ECM, TCC solenoid and control circuitry are functioning correctly and TCC still does not apply properly, problem may be hydraulic or mechanical. See appropriate AUTO TRANS OVERHAUL article.

Fig 1: Chart C-8B, 4T60 TCC Troubleshooting 1 Of 2 (3.3L PFI A Body)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Chart C-8B, 4T60 TCC Troubleshooting 2 Of 2 (3.3L PFI A Body)

Courtesy of GENERAL MOTORS CORP.