Cooling Fan Control Signal

Description
The electric cooling fan(s) are used to cool engine coolant flowing through the radiator. They are also used to cool the refrigerant flowing through the A/C condenser.

Operation
The electric cooling fan(s) are controlled by the PCM. The PCM controls the ground path for the three cooling fan relays. The relay(s) are used to control the high current flow to power the cooling tan motors. When minimum cooling is required, the PCM will energize cooling fan relay #1 and since both fans are connected in series through the Mode Control relay, both fans will operate at low speed. When maximum cooling is required, the PCM energizes all three cooling fan relays. Power is supplied to the left fan through cooling fan relay #1 and is grounded through the Mode Control relay. The right fan is powered directly through cooling fan relay #2 causing both fans to operate at high speed.

Low Speed Cooling Fans
The low speed cooling fans are controlled by the PCM based on the following inputs:

^ The A/C system.
^ The Engine Coolant Temperature (ECT) sensor.
^ The Vehicle Speed Sensor (VSS).

The PCM will turn the low speed cooling fans ON when any of the following conditions exist at idle:

^ Certain PCM Diagnostic Trouble Codes (DTCs) are set.
^ ECT above 106° C (223° F) will enable low speed fans.

Once the low speed fans are turned ON by Engine Coolant Temperature , the PCM will turn the fans OFF when that temperature has dropped about 3°C (5°F).

High Speed Cooling Fans
The High Speed Cooling Fans are controlled by the PCM based on the following inputs:

^ The A/C system
^ The Engine Coolant Temperature (ECT) sensor
^ The Vehicle Speed Sensor (VSS).

The PCM will turn the secondary cooling fan ON when any of the following conditions exist at idle:

^ Certain PCM Diagnostic Trouble Codes (DTCs) set.
^ ECT above 151°C (304°F).

Once the high speed cooling fans are turned ON by the Engine coolant temperature, the PCM will turn the fans OFF when that temperature has dropped about 3°C (5°F).

The driver side of the cooling fan relays (Coil side of relay) will be diagnosed using DTCs P0480 and P0481. Refer to Electric Cooling Fan Diagnosis / System Diagnostic Charts for the contact side of the fan circuit. Testing and Inspection

When a replacement of a cooling fan relay is necessary, the following relay(s) can be found in the under hood electrical center:

^ Fan control relay #1 (4).
^ Fan control relay #2 (2).
^ Mode control relay (3).

Engine cooling system component replacement can be found in the Cooling System.