* Blower Motor Resistor: This is the most common cause. The resistor is a component that regulates the speed of the blower motor. It often fails in a way that only the higher speeds work because they bypass part of the resistor. The resistor is usually located behind the glove box. You'll need to remove the glove box to access it. It's relatively inexpensive and easy to replace.
* Blower Motor Switch: The switch itself could be faulty. A problem in the switch's internal circuitry could prevent power from reaching the motor on the lowest speed. This is less common than the resistor issue.
* Wiring and Connections: Check the wiring harness leading to the blower motor and the resistor. Look for any loose connections, broken wires, or corrosion. A poor connection can interrupt the current at low speeds.
* Blower Motor: While less likely, a failing blower motor could also be the problem. Sometimes, a motor that's nearing the end of its life struggles to start at low speeds but can operate at higher speeds when more power is applied. This is usually accompanied by other signs like unusual noises.
* Fuse: Although less probable given it works on higher settings, a blown fuse specifically for the lowest blower motor speed setting is possible, especially if there's a short circuit somewhere in the system. Check your fuse box (usually under the hood or inside the cabin) for a blown fuse related to the HVAC system.
Troubleshooting Steps:
1. Check the Fuse: Start by checking the relevant fuse(s) in your fuse box.
2. Access the Blower Motor Resistor: Remove the glove box to access the resistor. Inspect it visually for any obvious damage (burn marks, etc.). Often, a simple wiggle test on the connectors might help. If you find a loose connection, that might be your problem.
3. Test the Resistor (Advanced): If visual inspection is inconclusive, you could use a multimeter to test the resistance values of the resistor to determine if it's faulty. You'll need to know the specific resistance values expected for each speed setting for your Impala model to do this properly (consult a wiring diagram).
4. Check Wiring: While you have the glove box out, carefully inspect the wiring harness for any damage or loose connections.
5. Test the Blower Motor Switch (Advanced): This requires more advanced electrical testing and is best left to a mechanic unless you're comfortable working with automotive electrical systems.
6. Consider the Blower Motor itself (Advanced): This is typically the last component to suspect and often requires professional diagnostic tools to determine if it's truly the problem.
If you're not comfortable working with car electrical systems, it's best to take your Impala to a qualified mechanic for diagnosis and repair. The blower motor resistor is the most likely culprit and is a relatively inexpensive and easy fix, making it a good starting point.
