The system might be failing if the fan runs constantly, never comes on, or runs intermittently when it shouldn't. Several things could cause this:
* Faulty Coolant Temperature Sensor (CTS): The most common cause. A malfunctioning CTS might send a signal to turn the fan on even when the engine isn't hot, or fail to send a signal even when it's overheating.
* Faulty Fan Relay: The relay acts as a switch, controlled by the CTS. A bad relay might not properly connect the power to the fan.
* Wiring Issues: A short circuit, a broken wire, or corroded connections in the wiring harness leading to the fan or the CTS can prevent the fan from working correctly.
* Faulty Fan Motor: The fan motor itself could be failing. It might draw excessive current, causing the relay to overheat and fail, or it might simply be seized or worn out.
* Low Coolant Level: If the coolant level is low, the engine will overheat faster and the fan will run more frequently, or even constantly. This is a symptom, not the cause. Low coolant needs to be addressed immediately.
To diagnose the problem, you'll likely need a multimeter to test the CTS, relay, and wiring for continuity and voltage. A mechanic can also use a scan tool to check for engine temperature readings and any related diagnostic trouble codes (DTCs) stored by the car's computer. Improperly functioning cooling systems can lead to engine damage, so diagnosing and fixing the issue promptly is crucial.
