GM Service Manual Online
For 1990-2009 cars only
GEN L-Terminal Signal Command: The scan tool displays On/Off. The scan tool displays Off until the engine is running, then the PCM supplies then the percentage value varies depending on electrical loads

Generator Lamp Circuit: The scan tool displays Fault/OK/Invalid State. The scan tool displays Fault until the ignition is placed into the ON position then OK is displayed.

Generator Lamp Command: The scan tool displays Yes/No. The scan tool displays Yes when the PCM grounds the charge indicator control circuit.

Ignition 1 Signal: The scan tool displays 0-20 Volts. The scan tool displays the voltage as received on the Ignition 1 circuit to the PCM.