Circuit Description

Ignition voltage is supplied directly to Fan Control (FC) relay coil. PCM controls the relay by grounding the control circuit through an internal switch called a driver. 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.

The relay is used to control the high current flow to the A/C compressor clutch, allowing the PCM driver to only have to handle the relatively low current used by the relay.