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.
The electric cooling fan(s) are controlled by the PCM.
The PCM controls the ground path for the cooling three cooling fan relay(s).
The relay(s) 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, and cooling
fan relay #2 is open. 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.
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 108°C (226°F) will enable low speed fans. |
| • | A/C head pressure above 248 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 3°C
(5°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 208 psi.
The minimum ON time for the low speed cooling fans is 50 seconds.
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 turn the secondary cooling fan ON when any of the following
conditions exist at idle:
| • | Certain PCM Diagnostic Trouble Codes (DTCs) set. |
| • | ECT above 112°C (234°F). |
| • | A/C head pressure above 248 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 3°C (5°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 208 psi. The minimum ON time for the high speed cooling fans is
30 seconds.
The driver side of the cooling fan relays (Coil side of
relay) will be diagnosed using DTCs P1641 and P1642. Refer to Electric Cooling Fan Diagnosis
for the contact side of the fan circuit.
Refer to Section 6B, Cooling and Radiator for component
replacement.
