General Description
The electric cooling fans are used to lower the temperature of the engine
coolant flowing through the radiator. They are also used to cool the refrigerant
(R134a) flowing through the A/C condenser.
Operation
The Powertrain Control Module (PCM) controls the operation of the cooling
fans. This is accomplished by providing a ground path for the cooling fan
relay coils within the PCM. The relay contacts will close and complete the
circuit between the the battery and the fan motors. Whenever there is a fan
ON request one or both fans will be running.
The cooling fan motors receive power from the following locations:
| - | Cooling Fan 1 receives power through the ECM BAT fuse and a 60 amp
maxifuse located in the Underhood Electrical Center 1. |
| - | Cooling Fan 2 receives power through the ECM IGN fuse and a 60 amp
maxifuse located in the Underhood Electrical Center 1. |
| - | During Fan 1 operation the PCM supplies a ground path for the
Fan 1 relay through the Output Driver Module (ODM) B Output 1. |
| - | During Fan 2 operation the PCM keeps Fan 1 energized and supplies a
ground path for the Fan 2 relay through Output Driver Module (ODM) B Output
2. |
| • | Underhood Electrical Center 1 - ECM BAT fuse and a 30 amp maxifuse. |
| • | Underhood Electrical Center 2 - Fan #3 fuse. |
| • | During low speed fans operation the PCM supplies a ground path
for cooling fan 1 relay through Output Driver Module (ODM) B output 1. This
energizes the fan 1 relay coil, closes the relay contacts, and supplies current
to the cooling fan 1 motor. The ground path for cooling fan 1 motor is through
the cooling fan 2 motor. The result is a series circuit with both cooling
fans running at low speed. |
| | During high speed cooling fan operation the PCM keeps cooling fan 1
relay energized. The PCM also supplies a ground path for cooling fan relays
2 and 3 through Output Driver Module (ODM) B output 2. This results in the
following actions: |
| • | Cooling fan 2 relay coil is energized. This supplies the cooling
fan 1 motor with its own engine ground. |
| • | Cooling fan 3 relay coil energizes, the relay contacts close,
and current is supplied to the cooling fan 2 motor. |
| • | During high speed fans operation, both engine cooling fan motors
have independent ground paths. |
The PCM will complete the ground path for the Fan 1 relay under the
following conditions:
| • | When engine temperature exceeds 100°C (212°F). |
| • | When A/C is requested (ambient temperature must be above 38°C
(100°F). |
| • | When A/C refrigerant pressure is greater than 190 psi. |
| • | When the ignition is off and engine coolant temperature is greater
than 106°C (222°F). |
Fan 2 is used for the increased demand on the cooling system due to
A/C. The PCM will complete the ground path for the Fan 2 relay under the following
conditions:
| • | When engine temperature exceeds 108° C (226° F). |
| • | When A/C refrigerant pressure is greater than 240 psi. |
When certain Diagnostic Trouble Codes (DTCs) are present, the PCM may
command the cooling fans to run all the time. It is important to perform the
Diagnostic Circuit check prior to diagnosing the engine cooling fans.
