GM Service Manual Online
For 1990-2009 cars only
Battery Voltage: The scan tool displays 0-17.5 volts. The scan tool displays the voltage as received by the BCM.

GEN F-Terminal Signal: The scan tool displays 0-100%. The scan tool displays a steady percentage value until the engine is running, then the percentage value varies depending on electrical loads

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 about 5 volts to the L - Terminal of the generator and the scan tool displays On.

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.

TR Sw.: The scan tool displays Park/Reverse/Neutral/Drive4/Drive3/Drive2/Drive1. The scan tool displays the current physical gear of the Trans Range switch.

Volt Lamp: The scan tool displays On/Off. The scan tool displays On when the IPC has been commanded by another module to command the Volt Lamp On.