Circuit Description

Voltage is applied to engine speed output circuit by the PCM. 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 a 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.