Corvette V8-5.7L VIN G (1997)
Accessory Signal: Description and Operation
PURPOSE
The electric cooling fan(s) are used to cool engine coolant flowing through the radiator. The fans are also used to cool the refrigerant flowing through
the A/C condenser.
OPERATION
The electric cooling fan(s) are controlled by the PCM. The PCM controls the ground path for the 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. The PCM will also enable the cooling fans after the ignition is turned off. When the engine coolant temperature exceeds 140°C (284°F) and the
ignition is turned off, the cooling fans will be enabled on low speed.
Low Speed Cooling Fans
The low speed cooling fans are controlled by the PCM based on the following inputs:
^
The A/C system.
^
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 104°C (219°F) will enable low speed fans.
^
A/C head pressure above 219 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 A/C system.
^
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 109°C (228°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 180 psi. The minimum ON time for the high speed cooling fans is 26 seconds.
The driver side of the cooling fan relays (Coil side of relay) will be diagnosed using DTCs P0480 and P0481. For component replacement, refer to
Cooling System.
