Engine Cooling Fan: Operation

Engine Control Module (ECM) uses primary and secondary cooling fan relays to control primary and secondary cooling fans. ECM uses input from A/C system, Engine Coolant Temperature (ECT) sensor, engine oil temperature sensor, Vehicle Speed Sensor (VSS) and engine RPM to energize primary cooling fan. With engine idling, ECM will energize primary cooling fan when certain ECM Diagnostic Trouble Codes (DTC's) are stored, Engine Coolant Temperature (ECT) sensor indicates greater than 219°F (104°C), engine oil temperature sensor indicates greater than 270°F (132°C) or A/C high side pressure is greater than 189 psi (13.3 kg/cm² ).

When ECM energizes primary cooling fan, minimum run time is 50 seconds. If ECM energized primary cooling fan because of excessive engine coolant temperature or engine oil temperature, primary cooling fan will be turned off when engine coolant temperature or engine oil temperature drops approximately 9°F (13°C). If ECM energized primary cooling fan because of excessive A/C head pressure, primary cooling fan will be turned off when A/C head pressure drops to 150 psi (10.5 kg/cm² ) or less.

ECM uses input from A/C system, Engine Coolant Temperature (ECT) sensor, engine oil temperature sensor, Vehicle Speed Sensor (VSS) and engine RPM to energize secondary cooling fan. ECM will energize secondary cooling fan when certain ECM DTC's are stored, ECT sensor indicates greater than 226°F (108°C), engine oil temperature sensor indicates greater than 277°F (136°C), or A/C head pressure is greater than 225 psi (16 kg/cm² ).

When ECM energizes secondary cooling fan, minimum run time is 26 seconds. If ECM energized secondary cooling fan because of excessive engine coolant temperature or engine oil temperature, secondary cooling fan will be turned off when engine coolant temperature or engine oil temperature drops approximately 9°F (13°C). If ECM energized secondary cooling fan because of excessive A/C head pressure, secondary cooling fan will be turned off when A/C head pressure drops to 189 psi (13.3 kg/cm² ), or less.