Cooling System: Description and Operation

Fuel Pump Relay:

PURPOSE
This car use an electric cooling fan. The fan is used for engine and A/C condenser cooling under certain conditions.

OPERATION
The electric cooling fan operates when the engine coolant temperature exceeds a certain value. The cooling fan on this engine is controlled by the Powertrain Control Module (PCM). The cooling fan has one speed. The PCM turns the cooling fan "ON," by grounding the coil of the fan relay when certain values are met. When A/C is requested, the cooling fan will be turned "ON."

When vehicle speed is above 35 mph, the PCM opens the ground circuit to the cooling fan relay because there should be sufficient air moving through the radiator to cool the engine. If A/C refrigerant pressure or engine coolant temperature become excessive or if a Diagnostic Trouble Code (DTC) is set, the PCM will turn the fan "ON" regardless of vehicle speed.


COOLING FAN RUN-ON
Under certain high temperature conditions the cooling fan will remain "ON" up to 7 minutes after the ignition is turned "OFF." This is called fan "Run-ON" and will occur if any of the following combinations of conditions exist as the ignition is turned "OFF."

^ Engine coolant temperature greater than 100°C (212°F) and Intake Air Temperature (IAT) greater than 80°C (158°F).
^ Engine coolant temperature greater than 112°C (233°F) and Intake Air Temperature (IAT) greater than 70°C (176°F).
^ Engine coolant temperature greater than 116°C (235°F).
The cooling fan will remain "ON" until these combinations of conditions no longer exist, up to a maximum of 7 minutes.
The PCM usually "powers down" 10 to 30 seconds after the ignition is turned "OFF."

Since the cooling fan is totally PCM controlled, the PCM remains "powered up" for up to 7 minutes after the ignition is turned "OFF" to provide the ground to energize the fan relay during fan "Run-On."

If the cooling fan is "OFF" after the ignition is turned "OFF," it will remain "OFF" regardless of temperatures, until the ignition is turned "ON."

DIAGNOSIS
The C-12 circuit chart will diagnose the PCM controlled cooling fan.
Chart C-12 Coolant Fan Functional Check