1. Faulty Radiator Fan Relay: This is often the culprit. The relay acts as a switch, turning the fan on and off based on signals from the PCM (Powertrain Control Module). A stuck relay will keep the fan running constantly. Testing the relay with a multimeter is relatively straightforward and a cheap part to replace.
2. Faulty Fan Motor: The fan motor itself could be malfunctioning. Worn-out brushes or a shorted winding can cause the fan to run continuously. This is more costly to repair, typically requiring replacement of the entire fan motor.
3. Problems with the PCM (Powertrain Control Module): Less common, but a faulty PCM can send incorrect signals to the fan relay, leading to continuous operation. This is the most expensive fix, and requires professional diagnosis.
4. Temperature Sensor Issues: The coolant temperature sensor (CTS) informs the PCM about the engine's temperature. A faulty CTS could give a false reading, making the PCM believe the engine is always overheating, thus keeping the fan on. This is a relatively inexpensive part to replace.
5. Low Coolant Level: While seemingly unrelated, extremely low coolant levels can trigger the fan to run continuously as a safety mechanism. Check your coolant level immediately.
6. Wiring Problems: Damaged or shorted wiring between the PCM, relay, and fan motor can also cause the fan to run constantly. This requires careful inspection and potentially rewiring.
7. Fan Switch (If Equipped): Some models have a manual fan switch. Make sure it isn't accidentally stuck in the "on" position.
Troubleshooting Steps:
1. Check coolant level: The simplest check first. Low coolant can cause issues.
2. Check the relay: This is the easiest and cheapest part to test and replace. A simple test with a multimeter will determine if it's stuck closed. Many online tutorials demonstrate this.
3. Inspect wiring: Look for any obvious damage or corrosion in the wiring harness related to the fan.
4. Test the coolant temperature sensor: Use a multimeter to check its resistance against the manufacturer's specifications.
5. If all else fails: Take it to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately.
Safety Note: Before working on any electrical components or the cooling system, allow the engine to cool down completely to avoid burns.
