I wish you'd posted your vehicle info so I knew what car you're working on
Here's the procedure for a 2000 Cavalier w/ 2.4L engine...
DTC P0480 Cooling Fan Relay Control Circuit
The electric cooling fan is controlled by the Powertrain Control Module (PCM) through the cooling fan relay based on inputs from the following components:
[*]Engine Coolant Temperature (ECT) sensor.[*]Intake Air Temperature (IAT) sensor.[*]A/C selector switch.[*]A/C refrigerant pressure sensor.[*]Vehicle Speed Sensor (VSS). [/ul]
The PCM controls the cooling fan by grounding the cooling fan control circuit which turns ON the cooling fan relay.
The cooling fan relay will be commanded ON when the following conditions are met:
[*]Engine coolant temperature reaches 106°C (223°F) or more.[*]A/C clutch requested.[*]Vehicle speed is less than 38MPH. [/ul]
The cooling fan relay will be commanded ON regardless of vehicle speed when the following conditions are met:
[*]A DTC is set that requests the coolant fan to be ON.[*]Engine coolant temperature is 151°C (304°F) or more.[*]A/C refrigerant pressure is high. [/ul]
The cooling fan may be commanded ON when the engine is not running under a fan Run-On conditions described in the Engine Cooling Fan Description - Electric
portion of the service manual.
Conditions for Running the DTC
[*]The engine is running.[*]The battery voltage is greater than 9.5volts. [/ul]
Conditions for Setting the DTC
[*]The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.[*]The condition must be present for a minimum of 6seconds. [/ul]
Action Taken When the DTC Sets
[*]The PCM will illuminate the Malfunction Indicator Lamp (MIL) after tow consecutive ignition cycles in which the diagnostic runs with the fault active.[*]The PCM will record the operating conditions at the time during which the diagnostic fails. This information will store in the Freeze Frame and/or Failure Records. [/ul]
Conditions for Clearing the MIL/DTC
[*]The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.[*]A history DTC will clear after 40 consecutive warm up cycles without a fault.[*]Use a scan tool to clears the DTCs. [/ul]
[*]If the cooling fan or cooling fan control circuit is shorted to ground the cooling fan fuse will open. An open cooling fan fuse will cause the DTC to set.[*]If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over, or if the Temp light, or temperature gage indicated overheating.[*]Check for the proper amount of coolant in the system.[*]If the gage, or light, indicates overheating, but no boil over is detected, the gage or light circuit should be checked. The gage accuracy can also be checked by comparing the engine coolant temperature sensor reading using a scan tool with the gage reading.[*]If the engine is actually overheating, and the gage indicates overheating, but the cooling fan is not coming ON, the Engine Coolant Temperature (ECT) sensor may have shifted out of calibration and should be checked. Refer to Temperature vs Resistance
for a Temperature vs. Resistance table.[*]If the engine is overheating, and the coolant fan is ON, the cooling system should be checked. Refer to the cooling and radiator of the service manual. [/ul]