Final answer:
GM Class 2 communication systems use 7 volts for active communication and 0 volts when idle, as part of vehicle onboard diagnostics.
Step-by-step explanation:
The GM Class 2 communication system utilizes a signaling method that toggles between two distinct voltage levels to transmit data. The correct voltages that the system alternates between are 7 volts and 0 volts. When the communication line is active and sending data, it switches to 7 volts. When the line is not sending data or is in the idle state, it sits at 0 volts. This system is a part of vehicle's onboard diagnostic systems and is critical for ensuring components within the vehicle are communicating properly.