The electric cooling fans are used to cool engine coolant
flowing through the radiator. The fans are also used to cool the refrigerant
flowing through the A/C condenser.
The electric cooling fans are controlled by the PCM. The PCM controls
the ground path for the 3 cooling fan relays. The relays are used
to control the high current flow to power the cooling fan motors. Both
fans operate together. When minimum cooling is required, the PCM energizes
cooling fan relay #1 and both fans operate at low speed, since the fans
are connected is series through cooling fan relay #3. Cooling fan relay
#2 and #3 are both OFF. When maximum cooling is required, the PCM energizes
all three cooling fan relays. The left fan is still powered through cooling
fan relay #1, but is now grounded through cooling fan relay #3. The right
fan is now powered directly through cooling fan relay #2 and both fans
operated at high speed.
The PCM will also enable the cooling fans after the ignition is turned
off. When the engine coolant temperature exceeds 140°C (284°F) and
the ignition is turned off, the cooling fans will be enabled on low speed.
Low Speed Cooling Fans
The low speed cooling fans are controlled by the PCM based on the following
inputs:
| • | 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 104°C (219°F) will enable low speed fans |
| • | A/C head pressure above 1510 kPa (219 psi) |
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 6°C
(11°F). If the low speed cooling fans are turned ON by high A/C head
pressure, the PCM will turn the fans OFF when the pressure has dropped
to 1034 kPa (150 psi). The minimum ON time for the low speed
cooling fans is 50 seconds.
When engine speed is above 3500 RPM for 12 seconds and
the engine oil temperature is above 127°C (261°F), the low speed cooling
fans will be turned ON.
High Speed Cooling Fans
The High Speed Cooling Fans are controlled by the PCM based on the following
inputs:
| • | The Engine Coolant Temperature (ECT) sensor |
| • | The Vehicle Speed Sensor (VSS) |
The PCM will enable high speed cooling for both fans when any of the
following conditions exist:
| • | Certain PCM Diagnostic Trouble Codes (DTCs) set |
| • | ECT above 109°C (228°F) |
| • | A/C head pressure above 1551 kPa (225 psi) |
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 6°C (11°F). If the high speed cooling fans are turned ON
by high A/C head pressure, the PCM will turn the fans OFF when the pressure
has dropped to 1241 kPa (180 psi). The minimum ON time
for the high speed cooling fans is 26 seconds.
