* Faulty Radiator Fan Relay: This is a common and relatively inexpensive fix. The relay acts as a switch, controlling the power to the fan. A faulty relay might keep the fan energized even when it shouldn't be.
* Bad Temperature Sensor: The engine's temperature sensor tells the vehicle's computer when to turn the fan on and off. If the sensor is malfunctioning and sending a consistently high temperature reading, the fan will run continuously.
* Faulty PCM (Powertrain Control Module): The PCM is the brain of the vehicle. A problem with the PCM itself could be sending the wrong signal to the fan, causing it to run constantly. This is a more serious and expensive issue.
* Short Circuit in the Wiring: A short in the wiring harness leading to the fan or relay can provide constant power, leading to the fan's continuous operation.
* Low Coolant Level: While it might seem counterintuitive, a low coolant level can sometimes trigger the fan to run constantly as the sensor detects overheating (even if the engine isn't actually overheating). Check your coolant level!
* Stuck Fan Switch (if equipped): Some vehicles have a manual switch for the fan. If this is stuck, the fan will remain on.
* Failing Fan Motor: In rare cases, a failing fan motor itself might cause it to run continuously, even if it's not receiving a signal to do so. This is less likely but possible.
Troubleshooting Steps:
1. Check Coolant Level: This is the easiest and first step. Low coolant can cause a false overheat condition.
2. Inspect the Relay: Locate the radiator fan relay (consult your owner's manual for location). You can often visually inspect it for obvious damage, or try swapping it with another relay of the same type (if possible) to see if the problem follows the relay.
3. Check the Temperature Sensor: This often requires a multimeter to test the sensor's resistance at various temperatures. A faulty reading would indicate a problem.
4. Examine the Wiring: Carefully inspect the wiring harness for any signs of damage, fraying, or shorts.
Important Note: If you're not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic for diagnosis and repair. Continuing to drive with a constantly running radiator fan could lead to further problems.
