1. Is the fan *supposed* to be running?
* Engine Temperature: The primary trigger is coolant temperature. If the engine is cold or only slightly warm, the fan shouldn't be running. Let the engine run until it reaches normal operating temperature (indicated by the temperature gauge). The fan *should* come on at this point.
* AC Use: The fan will also run when the air conditioning is on, regardless of engine temperature. Try turning the AC on to see if the fan activates.
* Low Coolant Level: A low coolant level can trigger the fan in some vehicles as a safety precaution. Check your coolant level.
2. Testing the System:
* Visual Inspection: Carefully inspect the fan itself for any obvious obstructions (like debris). Also check the fan shroud (the plastic housing around the fan) for damage.
* Relay Check: The cooling fan is controlled by a relay. There might be one or two relays depending on your model – a relay for the low speed and a relay for the high speed. You'll need to locate the relay(s) in the fuse box (usually under the hood). You can:
* Visually inspect: Look for any obvious signs of damage or corrosion.
* Swap the relay: If you have a spare relay of the same amperage rating, swap it with the suspected cooling fan relay. If the fan now works, the relay was faulty.
* Fuse Check: There's also a fuse associated with the cooling fan circuit. Check the fuse box diagram to find the correct fuse and test it with a multimeter or replace it if it's blown.
* Wiring Check: This is more advanced and requires electrical knowledge. You can check the wiring harness leading to the fan and the relay for any broken wires, corrosion, or loose connections. A multimeter is needed to test for voltage and continuity. Trace the wiring from the fan motor, to the relay, and to the engine control module (ECM).
* Coolant Temperature Sensor: A faulty coolant temperature sensor can prevent the fan from turning on. The ECM uses the sensor's reading to determine when to engage the fan. This sensor will need to be tested with a multimeter. Replacing it is usually relatively inexpensive.
* Engine Control Module (ECM): As a last resort, a problem within the ECM can be a cause. This is the least likely, and usually the most expensive and involved repair.
3. If the fan runs only at high speed:
This usually points to a faulty low-speed relay or a problem within the wiring for the low-speed circuit.
4. Important Safety Note:
* Hot Engine: Let the engine cool down completely before doing any hands-on work. The radiator, hoses, and engine components will be extremely hot and can cause burns.
If you're not comfortable performing these checks yourself, it's best to take your vehicle to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and efficiently. Provide them with the information you've gathered from your checks, as it will assist them in their diagnosis.
