Circuit Description

The powertrain control module (PCM) creates the vehicle speed output signal by pulsing the circuit to ground. The PCM monitors the voltage on the vehicle speed output circuit. If the PCM determines that the voltage is out of the normal operating range, a DTC sets.

Various components apply a voltage to the vehicle speed output circuit. The 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 vehicle speed sensor (VSS) signal input. The various components recognize the voltage being pulled to ground as an indication of vehicle speed. The PCM 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). If the fault detection circuit senses a voltage other than what is expected, the fault line status changes causing DTC P0608 to set.