* Faulty Cooling Fan Relay: This is the simplest and cheapest possibility. The relay controls the power to the cooling fan. A malfunctioning relay could send power to the fan continuously, regardless of engine temperature.
* Bad Cooling Fan Control Module (CFCM) or PCM (Powertrain Control Module): The CFCM (if equipped) or the PCM receives temperature readings from sensors and controls the fan accordingly. A malfunctioning unit might send the "fan on" signal constantly. The PCM is more likely to be the culprit if other engine systems are behaving erratically.
* Shorted Wiring: A short circuit in the wiring harness supplying the cooling fan could also cause it to run continuously. This could be due to damaged insulation, rodent damage, or a corroded connection.
* Faulty Coolant Temperature Sensor (CTS): This sensor tells the PCM/CFCM the engine's temperature. A faulty CTS could send a false reading (e.g., always indicating overheating), triggering the fan.
* Low Coolant Level: While less likely to cause a *constantly* running fan, a very low coolant level can cause the engine to overheat, which in turn would keep the fan running. Check your coolant level immediately.
* Head Gasket Failure (less likely but serious): A blown head gasket could allow coolant to leak into the cylinders or vice versa, leading to overheating and a constant fan operation. This is a more serious issue with potentially more expensive repairs.
Troubleshooting Steps:
1. Check the coolant level: This is the first thing to do. Low coolant is a serious issue regardless of the fan.
2. Inspect the wiring: Look for any obvious signs of damage to the wiring harness leading to the cooling fan.
3. Check the cooling fan relay: This is usually a simple relay you can swap out for a known good one. An auto parts store can help identify the correct relay.
4. Check the CTS: This is often a relatively inexpensive part that is easy to replace. You can test the sensor with a multimeter to verify its readings.
5. Obtain diagnostic trouble codes (DTCs): Use an OBD-II scanner to retrieve any stored trouble codes from the PCM. These codes can provide valuable clues about the cause of the problem. This is essential to further diagnose.
6. Professional Diagnosis: If you're not comfortable tackling electrical troubleshooting, take your Sunfire to a qualified mechanic for diagnosis and repair. This is especially important if you suspect a head gasket issue or PCM problems. A blown head gasket is a serious repair requiring extensive mechanical skill.
The constantly running fan could cause significant wear and tear on the fan motor, so addressing the underlying problem is crucial. Don't continue driving the car with this issue unless absolutely necessary. Overheating can cause serious engine damage.
