Diagnostic Aids

The "Scan" tester only indicates when the ECM has turned on the TCC driver. This does not confirm that the TCC has engaged. To determine if TCC is functioning properly, observe engine RPM. RPM should decrease when "Scan" tester indicates TCC driver has turned.

Fig 1: Chart C-8A, TCC Troubleshooting Chart 1 Of 3 (3.1L PFI A & W Bodies)

Courtesy of GENERAL MOTORS CORP.

1. Some "Scan" testers display the gear switch state in different manners. Refer to manufacturer's operating manual for additional information. Since both switches should be in the closed state during this test, scan should read the same for either 3rd or 4th gear switch.
2. Determines whether the switch or signal circuit is open. The circuit can be checked for an open by measuring voltage at the TCC connector. Reading should be about 12 volts.
3. Because switch should be grounded in this step, disconnecting TCC connector should cause "Scan" tester display to change state.
4. Switch state should change when vehicle shifts into 3rd gear.

Fig 2: Chart C-8A, TCC Troubleshooting Chart 2 Of 3 (3.1L PFI A & W Bodies)

Courtesy of GENERAL MOTORS CORP.

If vehicle is road tested for a TCC related problem, ensure the switch state does not change while in 4th gear because the TCC will disengage. If switch changes state, carefully inspect wire harness/routing and connections.

Fig 1: Chart C-8A, TCC Troubleshooting Chart 3 Of 3 (3.1L PFI A & W Bodies)

Courtesy of GENERAL MOTORS CORP.