Converter Lock-Up Signal From ECM

Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
Connect a test light to battery voltage. Touch TCC control driver terminal with test light. See Fig 1. Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty ECM connector or ECM. On some models, lock-up signal may be checked at ALDL terminal "F" instead of at ECM terminal.

Fig 1: 3.1L Torque Converter Clutch Schematic

Courtesy of GENERAL MOTORS CORP.