Engine Fan Running When Car is Off

Causes

There are several possible causes of the engine fan running when the car is off:

Coolant temperature sensor is faulty. This sensor tells the engine control module (ECM) the temperature of the coolant. If the sensor is faulty, it may send a false signal to the ECM, causing the fan to run even when the engine is off.
ECM is faulty. The ECM controls the operation of the engine fan. If the ECM is faulty, it may send a false signal to the fan, causing it to run even when the engine is off.
Fan relay is stuck closed. The fan relay is a switch that turns the fan on and off. If the relay is stuck closed, the fan will run even when the engine is off.
Wiring problem. A wiring problem can cause the fan to run even when the engine is off. For example, a short circuit in the wiring harness could cause the fan to run constantly.

Diagnosis

To diagnose the cause of the engine fan running when the car is off, you will need to perform the following steps:

Check the coolant temperature sensor. The coolant temperature sensor is located on the engine. Disconnect the sensor and measure the resistance between the terminals. The resistance should be within the specified range for the sensor. If the resistance is not within the specified range, the sensor is faulty and should be replaced.
Check the ECM. The ECM is located under the dashboard. Remove the ECM and inspect it for any signs of damage. If the ECM is damaged, it will need to be replaced.
Check the fan relay. The fan relay is located in the fuse box. Remove the relay and inspect it for any signs of damage. If the relay is damaged, it will need to be replaced.
Check the wiring harness. Inspect the wiring harness for any signs of damage. If the wiring harness is damaged, it will need to be repaired or replaced.

Repair

Once you have diagnosed the cause of the engine fan running when the car is off, you can repair the problem. The repair will depend on the cause of the problem.

If the coolant temperature sensor is faulty, replace the sensor.
If the ECM is faulty, replace the ECM.
If the fan relay is stuck closed, replace the relay.
If the wiring harness is damaged, repair or replace the wiring harness.

Prevention

There are several things you can do to prevent the engine fan from running when the car is off:

Keep the coolant level full. A low coolant level can cause the engine to overheat, which can cause the fan to run even when the engine is off.
Have the cooling system serviced regularly. A well-maintained cooling system will help to prevent the engine from overheating.
Avoid driving in hot weather. If you must drive in hot weather, try to keep the car in a shaded area as much as possible.

Conclusion

If the engine fan is running when the car is off, it is important to diagnose and repair the problem as soon as possible. A running fan can drain the battery and cause the engine to overheat.