The engine cooling fan system consists of two electric
cooling fans and three fan relays that are controlled by the PCM. The cooling
fans receive power from a 50A Maxifuses located in the Underhood Fuse Block
Assembly. The relays are wired in a series/parallel arrangement that allows
the PCM to operate both fans together at low and/or high speed.
During low speed operation, the PCM supplies a ground path for the low
speed fans relay through the low speed fans control circuit. This energizes
the relay coil, closes the relay contacts, and supplies current to the engine
cooling fans. The ground path for the right engine cooling fan is through
the series/parallel cooling fan relay and the left engine cooling fan.
The result is a series circuit with both fans running at low speed.
To command high speed cooling fan operation the PCM first supplies the
ground path for the low speed cooling fans relay through the low speed fans
control circuit. After a few seconds delay, the PCM supplies the ground
path for the high speed cooling fan relay and the series/parallel cooling
fan relay through the high speed fans control circuit. During high speed
operation, both engine cooling fans are supplying current through their
respective maxifuse and each fan has its own ground path.
PCM will command fan operation under the following conditions:
Low Speed Fan Operation
| • | Engine coolant temperature exceeds approximately 106°C (229°F). |
| • | Transmission fluid temperature exceeds 150°C (302°F). |
| • | A/C operation is requested. |
| • | After the vehicle is shut OFF if the coolant temperature at key-off
is more than 151°C (304°F) and system voltage was more than 12 volts.
The fans will stay ON for approximately 3 minutes. |
The fans will switch from low to OFF when the coolant drops below 102°C
(216°F).
High Speed Fan Operation
| • | Engine coolant temperature reaches 112°C (234°F). |
| • | Transmission temperature is more than 151°C (304°F). |
The fans will switch from high to low (except when DTCs set) when the
coolant drops below 106°C (229°F).
