Car Fan Stays On After Turning Engine Off

Causes

There are several possible causes for the car fan to stay on after the engine is turned off:

Coolant temperature sensor failure: The coolant temperature sensor tells the engine control module (ECM) how hot the engine is. If the sensor fails, the ECM may not realize that the engine has cooled down and keep the fan running.
ECM failure: The ECM is responsible for controlling the fan. If the ECM fails, it may not be able to turn off the fan.
Relay failure: The relay is a switch that turns the fan on and off. If the relay fails, the fan may stay on even after the ECM has turned it off.
Wiring problem: A wiring problem can cause the fan to stay on even after the engine is turned off.

Diagnosis

To diagnose the cause of the car fan staying on after the engine is turned off, you will need to:

Check the coolant temperature sensor: Start the engine and let it idle. Use a voltmeter to check the voltage at the coolant temperature sensor. The voltage should be between 0 and 5 volts. If the voltage is out of range, the sensor may be faulty.
Check the ECM: If the coolant temperature sensor is working properly, the next step is to check the ECM. You can do this by using a scan tool to check for any trouble codes. If there are any trouble codes, they may indicate a problem with the ECM.
Check the relay: The relay is located in the fuse box. You can check the relay by swapping it with another relay of the same type. If the fan turns off after you swap the relay, the old relay was faulty.
Check the wiring: If the coolant temperature sensor, ECM, and relay are all working properly, the next step is to check the wiring. You can do this by using a multimeter to check for any breaks or shorts in the wiring.

Repair

Once you have diagnosed the cause of the car fan staying on after the engine is turned off, you can repair the problem. The repair may involve replacing the coolant temperature sensor, ECM, relay, or wiring.

If you are not comfortable performing the repairs yourself, you can take your car to a mechanic for repairs.

Prevention

There are several things you can do to prevent the car fan from staying on after the engine is turned off:

Keep the coolant level full: A low coolant level can cause the coolant temperature sensor to fail.
Have the coolant system serviced regularly: A clogged coolant system can cause the coolant temperature sensor to fail.
Inspect the wiring: Regularly inspect the wiring for any breaks or shorts.

By following these tips, you can help to prevent the car fan from staying on after the engine is turned off.