* Faulty Fan Control Module (FCM) or Relay: The FCM or relay is responsible for controlling when and which fan operates. A malfunctioning component could cause both fans to run continuously, regardless of engine temperature. This is a common culprit.
* Faulty Temperature Sensor: The engine's temperature sensor provides the FCM with information about the coolant temperature. If the sensor is faulty and constantly reporting high temperature (or shorted to ground), the FCM will activate both fans to compensate.
* Wiring Issues: A short circuit or damaged wiring in the fan circuit could cause a constant power supply to both fans. This could be anywhere from the sensor to the fans themselves.
* Stuck Fan Relays: If the relays themselves are mechanically stuck closed, they will continuously provide power to the fans.
* Low Coolant: While it may seem obvious, low coolant will cause the engine to overheat, triggering both fans to run constantly. Check your coolant level in the overflow tank and radiator.
* Faulty Fan(s): Although less likely to cause *both* fans to run constantly, a faulty fan motor can draw excessive current, potentially triggering the FCM to run both fans.
* PCM Issues (less likely): In some systems, the Powertrain Control Module (PCM) plays a role in fan control. While less common, a faulty PCM could also lead to this issue.
Troubleshooting Steps:
1. Check Coolant Level: The simplest check first. Low coolant will lead to overheating and constant fan operation.
2. Inspect Wiring: Carefully examine the wiring harness leading to the fans and the FCM/relays for any signs of damage, chafing, or shorts.
3. Test the Temperature Sensor: You'll need a multimeter to test the sensor's resistance at various temperatures. Consult your vehicle's repair manual for the proper resistance values.
4. Check the Fan Relays: Listen closely to the relays when the fans are running. A clicking sound indicates normal operation. If a relay is consistently "on" without clicking, it may be stuck.
5. Test the Fan Control Module (FCM): This usually requires more advanced diagnostic tools, often a scan tool that can read data from the vehicle's computer.
6. Test the Fans Themselves: Check if each fan operates when directly connected to power (with extreme caution, as this can damage the fans if done incorrectly). This helps determine if a fan itself is faulty.
If you're not comfortable performing these checks yourself, it's best to take your Buick Regal to a qualified mechanic for diagnosis and repair. Continuing to drive with both fans running constantly can lead to further damage.
