When is the code detected?If the fault detection circuit senses a voltage other than what is expected, the fault line status changes causing the P0608 to set.
P0608 Chevrolet DescriptionVarious components apply a voltage to the Vehicle Speed Output circuit. The Powertrain Control Module (PCM) creates the Vehicle Speed Output signal by rapidly grounding this circuit via an internal switch called a driver. The driver operates at the same rate as the VSS signal input. The various components recognize the voltage being pulled to ground as an indication of vehicle speed.
The driver supplies the ground for the component being controlled. Each driver has a fault line which the PCM monitors. When the PCM commands a component ON, the voltage of the control circuit should be low (near 0 volts). When the PCM commands the control circuit to a component OFF, the voltage potential of the circuit should be high (near battery voltage).