Circuit Description

Voltage is applied to Vehicle Speed Sensor (VSS) output circuit by the various components which use vehicle speed data. PCM creates the VSS output signal by rapidly grounding this circuit through an internal switch called a driver. The driver operates at the same rate as the low resolution signal input. Other components on this circuit recognize the voltage being pulled to ground as an indication of engine speed.

The primary function of the driver is to supply ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When PCM is commanding a component on, the voltage on the control circuit should be low (near zero). When PCM is commanding a component off, the voltage of the circuit should be high (near battery voltage). If the fault detection circuit senses a voltage other that what is expected, the fault line will change causing DTC to set.