* Faulty Photoelectric Sensor: This sensor detects the brightness of headlights from behind. If it's malfunctioning, it won't send the correct signal to darken the mirror. This is the most common cause of failure. Unfortunately, this sensor is integrated into the mirror assembly itself, meaning you can't replace it separately.
* Internal Wiring or Electrochromic Layer Failure: The wiring within the mirror or the electrochromic layer itself could be damaged or degraded. Again, this is an internal component and not easily repairable.
* Power Supply Issue: Though less likely, a problem with the power supply to the mirror could prevent it from dimming. Check the fuse related to the rearview mirror (consult your owner's manual). A faulty connection in the wiring harness is also a possibility but less probable.
In short: There's no practical DIY repair for a malfunctioning auto-dimming rearview mirror in a 2003 Chevy Impala LS. The entire mirror assembly needs to be replaced.
Here's what you should do:
1. Check the fuse: Consult your owner's manual to locate and check the fuse related to the rearview mirror. Replacing a blown fuse is the easiest and cheapest first step.
2. Replace the mirror assembly: If the fuse is fine, your only realistic option is to replace the entire auto-dimming rearview mirror. You can find replacement mirrors online (e.g., eBay, Amazon, parts websites) or at auto parts stores. Ensure you get one specifically designed for a 2003 Chevy Impala LS. Installation is relatively straightforward, usually involving unclipping the old mirror and clipping the new one in place.
3. Consider a non-auto-dimming replacement: If the cost of a replacement auto-dimming mirror is too high, you can opt for a standard, non-auto-dimming rearview mirror. This is a cheaper alternative, but you'll lose the auto-dimming feature.
Remember to always disconnect the negative battery terminal before attempting any electrical work on your vehicle. If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic.
