* Stuck Relay: The relay that controls the blower motor may be sticking, failing to open the circuit even after the ignition is off. This is a common culprit.
* Faulty Blower Motor Resistor: While the resistor controls fan speed, a faulty one can sometimes cause the motor to run continuously. A short circuit within the resistor can bypass the normal control circuit.
* Wiring Issues: A short circuit or a wire that's touching ground in the wiring harness controlling the blower motor could keep power flowing to it. This is often a result of wear, damage, or corrosion.
* Faulty Ignition Switch: Although less likely, a problem with the ignition switch itself could be preventing the power to the blower motor from being completely cut off.
* Body Control Module (BCM) Problem (Less Likely): In some vehicles, the BCM controls various functions, including the blower motor. A malfunctioning BCM could be sending the wrong signal. This is less likely but possible.
Troubleshooting Steps:
1. Check the Relay: Locate the blower motor relay (consult your owner's manual or a wiring diagram). Try swapping it with a known good relay of the same type (if you have one). If the problem goes away, the relay is faulty.
2. Inspect the Blower Motor Resistor: Locate the resistor (often under the dash) and visually inspect it for any signs of damage or burning. If it looks damaged, it should be replaced.
3. Check the Wiring: Carefully inspect the wiring harness leading to the blower motor and the relay for any signs of damage, fraying, or corrosion. Repair or replace any damaged wires.
4. Listen Carefully: When the problem occurs, listen carefully around the blower motor and its associated components. A clicking or buzzing sound might pinpoint the source of the problem (e.g., a bad relay).
If you are not comfortable working with car electrical systems, it's best to take your Buick to a qualified mechanic to diagnose and repair the issue. Attempting repairs without proper knowledge can lead to further damage or even injury.
