Circuit Description

Ignition voltage is supplied directly to cooling fan relay coil. PCM controls relay by grounding control circuit through an internal switch called a driver. Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM.

When PCM is commanding a component ON, voltage of control circuit should be low (near zero volts). When PCM is commanding control circuit to a component OFF, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, fault line status will change, causing DTC to set.

DTC will set when the following conditions are present:

• Engine speed greater than 400 RPM.
• Ignition voltage between 6-18 volts.
• PCM detects commanded state of driver and actual state do not match.
• Conditions met for 5 seconds.