Functional Check - Electric Cooling Fan

Circuit Description

The electric cooling fan(s) are controlled by the PCM The PCM controls the around path for the three cooling fan relays. The relay(s) are used to control the high current flow to power the cooling fan 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 Ian is powered directly through cooling Ian relay #2 causing both fans to operate at high speed.

Cooling Fan Run-On

The PCM usually powers down 10 to 30 seconds after the ignition is turned OFF. Since the cooling fan is PCM controlled, the PCM may remain powered up for up to 7 minutes after the ignition is turned OFF to provide a ground in order to energize the cooling fan relay.

This is called a fan Run-On and will occur it any of the following combinations of conditions exist when the ignition is turned OFF.

^ Engine coolant temperature greater than 100°C (212°F) and intake air temperature greater than 80°C (176°F).
^ Engine coolant temperature greater than 112°C (234°F) and intake air temperature greater than 70°C (158°F).
^ Engine coolant temperature greater than 116°C (241°F).

The PCM and cooling fan will remain ON until these combinations of conditions no longer exist, up to a maximum of 7 minutes.

If the cooling fan is OFF when the PCM powers down, it will remain OFF regardless of any temperatures until the ignition is turned ON again.

Diagnostic Aids

If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over, or the warning indicator light. If the engine is actually overheating but the cooling fan is not coming ON, the Engine Coolant Temperature (ECT) sensor has probably shifted out of calibration and should be replaced.

If the engine is overheating and the cooling fans are ON, the cooling system should be checked, refer to the cooling system. The PCM will command low speed fans ON at 106°C (223°F) and OFF at 103°C (217°F) and, high speed fans ON at 151°C (304°F) and OFF at 151°C (304°F)

Test Description

Number(s) below refer to number(s) on the diagnostic table.

2. The PCM will enable the engine cooling fans when certain Diagnostic Trouble Codes are set Go to applicable DTC Table first before proceeding with this table.
3. Allow the engine coolant temperature to cool below 100°C (212°F) before proceeding with diagnosis.