Operation
The Engine Coolant Fans receive power from two separate 30 amp maxifuses
located in the Underhood Electrical Center.
During low speed operation, the PCM supplies a ground path for the Cool
Fan 1 relay through the Low Speed Fans control circuit. This energizes the
relay coil, closes the Fan 1 relay contacts, and supplies current to engine
cooling fan #1 motor. The ground path for engine cooling fan #1 is through
the series/paralles cooling fan relay (Cool Fan 2 Relay) and engine cooling
fan #2 motor. The result is a series circuit with both fans running at low
speed.
To command high speed cooling fan operation, the PCM first supplies
a ground path for the low speed cooling fan (Cool Fan 1) relay through the
Low Speed Fans Control circuit. After a 3 seconds delay, the PCM
supplies a ground path for the series/parallel (Cool Fan 2 Relay) and the
high speed cooling fan (Cool Fan #3) relays through the High Speed Fans
Control circuit. During high speed operation, both engine cooling fans are
supplied current from through their respective maxifuse and each fan has
its own ground.
Important: 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
Powertrain On-Board Diagnostic System check prior to diagnosing the engine
cooling fans.
The PCM will complete the ground path for cooling fan relay #1 under
any of the following conditions:
VIN K
| • | When engine coolant temperature exceeds 106°C (223°F). |
| • | When A/C is requested and ambient temperature is greater than
50°C (122°F). |
| • | When A/C refrigerant pressure is greater than 190 psi (2 volts). |
| • | When the ignition is off and engine coolant temperature is greater
than 140°C (284°F). |
VIN 1
| • | When engine coolant temperature exceeds 100°C (212°F). |
| • | When A/C is requested and ambient temperature is greater than
40°C (104°F). |
| • | When A/C refrigerant pressure is greater than 190 psi (2 volts). |
| • | When the ignition is off and engine coolant temperature is greater
than 140°C (284°F). |
For high speed cooling fans operation, the PCM will delay control of
the Cool Fan 2 Relay and Cool Fan #3 relay for 3 seconds. The 3 second
delay ensures that the cooling fan electrical load will not exceed the capacity
of the system. The PCM will complete the ground paths for cooling fan relays
Cool Fan #1, Cool Fan #2 Relay and Cool Fan #3 under any of the following
conditions:
VIN K
| • | When engine coolant temperature exceeds 110°C (230°F). |
| • | When A/C refrigerant pressure is greater than 240 psi (2.5 volts). |
VIN 1
| • | When engine coolant temperature exceeds 108°C (226°F). |
| • | When A/C refrigerant pressure is greater than 240 psi (2.5 volts). |
