1. Check the Blower Motor Resistor:
* Location: The resistor is usually located behind the glovebox or under the dashboard, often near the blower motor itself. Consult your Impala's repair manual for the precise location.
* Function: The resistor regulates the blower motor speed. If it fails, it can cause the motor to run at full speed constantly. A common failure mode is the resistor overheating and short-circuiting, leading to continuous operation.
* Inspection: Once located, visually inspect the resistor for any signs of burning, melting, or damage. If it looks burnt or damaged, it needs replacement.
2. Check the Blower Motor Control Module (HVAC Control Module):
* Location: This module is typically located under the dashboard, often near the HVAC controls. Again, your repair manual is your best friend here.
* Function: This module controls the blower motor speed and other aspects of the climate control system. A faulty module can send signals to the motor to run continuously.
* Inspection: Visual inspection is less helpful here. Often, a faulty module requires professional diagnosis with a scan tool to check for error codes.
3. Check the Wiring:
* Look for shorts: Carefully examine all the wiring connected to the blower motor, resistor, and control module. Look for any frayed wires, damaged insulation, or signs of shorts. Pay close attention to the power wire supplying the blower motor. A short circuit to the power source will keep it running.
* Trace the wiring: Follow the wiring harness to make sure there are no loose connections or broken wires anywhere along its route.
4. Check the Blower Motor Switch:
* Possible culprit: While less common, a faulty blower motor switch can sometimes cause the problem. If the switch is stuck in the "on" position internally, the blower will remain running. This is usually diagnosed by eliminating other possible causes first.
5. Battery Disconnect:
* Immediate Stop: As a temporary measure to prevent battery drain, disconnect the negative terminal of your car battery. This will stop the blower motor, but it won't fix the underlying problem.
Important Considerations:
* Repair Manual: A repair manual specific to your 2004 Chevy Impala will be incredibly helpful in locating components and understanding the wiring diagrams. You can find these online (often as PDFs) or at auto parts stores.
* Safety: Working on car electrical systems can be dangerous. Disconnect the battery's negative terminal before starting any work.
* Professional Help: If you're not comfortable working with car electrical systems, take your Impala to a qualified mechanic for diagnosis and repair.
By systematically checking these components, you should be able to pinpoint the cause of your constantly running blower motor. Remember safety first and consult your repair manual for specifics on your vehicle's HVAC system.
