Engine Cooling Fan Description - Electric. Oldsmobile Shelby Series 1 1999

For 1990-2009 cars

The electric cooling fans 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.

The electric cooling fans are controlled by the PCM. The PCM controls the ground path for the three cooling fan relays. The relays 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 in series through cooling fan relay #3. Cooling fan relay #2 is open (not energized) and is not used for low speed operation of the fans. 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 113°C (235°F) and the ignition is turned off, the cooling fans will be enabled on low speed for 150 seconds.

### 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 cooling fans on low speed when any of the following conditions exist at idle:

• | Certain PCM diagnostic trouble codes (DTCs) are set.

• | The ECT above 108°C (226°F)

• | The A/C high side pressure above 215 psi

Once the low speed fans are turned ON by ECT, the PCM will turn the fans OFF when that temperature has dropped about 4°C (7°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 190 psi. The minimum ON time for the low speed cooling fans is 50 seconds.

The cooling fans are turned OFF at certain vehicle speeds. Adequate airflow through the A/C condenser and radiator occurs with vehicle movement to properly cool the A/C refrigerant and engine coolant without the assistance of the cooling fans.

### 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 enable both fans on high speed when any of the following conditions exist:

• | Certain PCM diagnostic trouble codes (DTCs) set

• | The ECT above 112°C (234°F)

• | The A/C high side pressure above 248 psi

Once the high speed cooling fans are turned ON by the ECT, the PCM will turn the fans OFF when that temperature has dropped about 4°C (7°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 208 psi. The minimum ON time for the high speed cooling fans is 30 seconds.