Here's a breakdown of why:
* Blower Motor Resistor Failure: The resistor is a series of resistances wired in a way to reduce the voltage going to the motor. When one or more of these resistances fail (often due to overheating), only the higher speeds (which bypass the faulty resistors) function correctly.
* Wiring Issues (Less Likely): While less common, a wiring problem between the resistor and the blower motor or the switch could also cause this. A broken wire or a bad connection would prevent lower speeds from working.
Troubleshooting Steps:
1. Locate the Blower Motor Resistor: This is usually located behind the glove compartment or under the dashboard. Consult your S10's repair manual for the precise location. It's often a small, rectangular component with several wires connected to it.
2. Visual Inspection: Once located, carefully inspect the resistor for any signs of burning, melting, or physical damage.
3. Resistance Testing (Advanced): If you have a multimeter, you can test the resistance of each resistor in the component to determine if any are open or have significantly changed value. (Consult a wiring diagram for proper testing procedures).
4. Check Wiring: Examine the wiring harness connected to the resistor and the blower motor for any signs of damage, fraying, or loose connections.
5. Replacement: If the resistor is visibly damaged or tests bad, replace it with a new one. You can usually find replacements at auto parts stores.
Important Note: Before working on your vehicle's electrical system, always disconnect the negative battery terminal to prevent accidental short circuits. If you're not comfortable working with car electronics, it's best to take it to a qualified mechanic.
