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 Engine Oil Temperature |
| • | 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. |
| • | Engine oil temperature above 132°C (270°F) |
| • | A/C head pressure above 189 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 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 Engine Oil Temperature |
| • | 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 109°C (228°F). |
| • | Engine oil temperature above 136°C (277°F) |
| • | A/C head pressure above 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 189 psi. The minimum ON time for the high speed cooling
fans is 26 seconds.
When engine speed is above 3500 RPM for 12 seconds and the engine
oil temperature is above 130°C (266° F), the high speed cooling fans
will be turned ON.
The following diagnostic table will diagnose the contact
side of the cooling fan relays. The driver side of the cooling fan relays
(Coil side of relay) will be diagnosed using DTCs P1641 and P1642.
Refer to Section 6B, Cooling and Radiator for component
replacement.
