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, monitor engine RPM. Engine RPM should decrease when the "Scan" tester indicates the TCC driver has turned on.

Fig 1: Chart C-8A, TCC Troubleshooting Chart 1 Of 2 (3.8L PFI C Body)

Courtesy of GENERAL MOTORS CORP.

1. Some "Scan" testers display the state of these switches in different ways. Be familiar with the type of tester being used. All switches should be in the closed state during this test, the tester should read the same for 2nd, 3rd and 4th gear switches.
2. Determines whether the switch or signal circuit is open. The circuit can be checked for an open by measuring the voltage (with a voltmeter) at the TCC connector. Voltage should be about 12 volts.
3. Because the switch should be grounded in this test, disconnecting the TCC connector should cause the "Scan" test switch state to change.
4. The switch state should change when the vehicle shifts into 2nd, 3rd and 4th gear.

If vehicle is road tested because of a TCC related problem, be sure the switch states do not change while in 4th gear, because the TCC will disengage. If switches change state, carefully check wire routing and connections.

Fig 1: Chart C-8A, TCC Troubleshooting Chart 2 Of 2 (3.8L PFI C Body)

Courtesy of GENERAL MOTORS CORP.