GM Service Manual Online
For 1990-2009 cars only
Battery Volts: The scan tool displays Volts. The scan tool displays the battery voltage received by the module.

GEN F-Terminal Signal: The scan tool displays 0%-100%. The scan tool displays 0%-20% until the engine is started and the PCM receives a variable signal from the generator. This value varies depending on electrical loads

GEN L-Terminal Signal: The scan tool displays Voltage/No Voltage. The scan tool displays Voltage until the engine is running, then No Voltage is displayed.

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.