For 1990-2009 cars

### General Description

The electric cooling fan(s) are used to cool engine coolant flowing through the radiator. They 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 cooling fan relay(s). The relay(s) are used to control the high current flow to power the cooling fan motors. The PCM determines operation of the independent fans based on various sensor inputs.

### Primary Cooling Fan (Fan 1)

The primary cooling fan is 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 primary cooling fan ON when any of the following conditions exist at idle:

• | Certain PCM Diagnostic Trouble Codes (DTCs) are set.

• | ECT above 107°C (225°F).

• | A/C head pressure above 225 psi.

Once the primary fan has been turned ON by the Engine Coolant Temperature (ECT) sensor, the PCM will turn the fan OFF when that temperature has dropped about 4°C (7°F). If the primary cooling fan has been turned ON by high A/C head pressure, the PCM will turn the fan OFF when the pressure has dropped to 180 psi. The minimum ON time for the primary cooling fan is 50 seconds.

### Secondary Cooling Fan (Fan 2)

The secondary cooling fan is 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 111°C (232°F).

• | A/C head pressure above 248 psi.

Once the secondary fan has been turned ON by the ECT, the PCM will turn the fan OFF when that temperature has dropped about 4°C (7°F). If the secondary cooling fan has been turned ON by high A/C head pressure, the PCM will turn the fan OFF when the pressure has dropped to 203 psi. The minimum ON time for the secondary cooling fan is 26 seconds.

Important: Vehicles equipped with option VO8 (Heavy Duty Cooling), will have one mechanical fan (primary) and one electric fan (secondary).

### Diagnosis

The following diagnostic table will diagnose the contact side of the cooling fan relays. The driver side of the cooling fan relays (Coil side of relay) will be diagnosed using DTCs P1641 and P1642.