The most likely culprits are:
* The fan's switch: A faulty switch that's stuck in the "on" position is a very strong possibility. This is the simplest and most common cause.
* The fan relay: The relay acts as a switch, controlled by the PCM (Powertrain Control Module) or a temperature sensor. A stuck relay will keep the fan running continuously.
* The temperature sensor: This sensor tells the PCM when to turn the fan on. A faulty sensor might send a signal indicating the engine is always overheating, even when it's not. This would keep the fan running constantly.
* The PCM (Powertrain Control Module): In rare cases, a problem within the PCM could cause the fan to run continuously. This is less likely, but possible.
* Wiring harness issue: A short circuit or damaged wiring in the fan circuit could cause the fan to remain on.
Troubleshooting Steps:
1. Check the fan switch: If your Cherokee has a manual switch for the fan (some models did), try disconnecting it to see if the fan stops. If it stops, the switch is the problem. If it continues running, the problem is elsewhere.
2. Locate the fan relay: This is typically a small box in a fuse box or relay center under the hood. You can visually inspect it for damage. You might try swapping it with another relay of the same amperage rating (as long as the other relay isn't critical). If the fan stops, you've likely found the faulty component.
3. Check the coolant temperature sensor: This is often located in the engine block or cylinder head. A multimeter can test the sensor's resistance to see if it's functioning properly. Consult a repair manual or online resources specific to your Jeep's engine for the correct testing procedure and resistance values.
4. Inspect the wiring: Carefully examine the wiring harness leading to the fan, relay, and sensor for any signs of damage, chafing, or shorts.
Important Note: Before doing any electrical work, disconnect the negative battery terminal to prevent accidental shorts or shocks.
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 run the fan will completely drain your battery.
