* Window Regulator Motor: The most common culprit is a failing window regulator motor. The clicking you hear is the motor trying to engage but failing to turn the gear mechanism that raises and lowers the window. This could be due to a worn-out motor, a lack of lubrication, or a burned-out armature.
* Window Regulator Gear: The plastic gears within the regulator mechanism are notorious for stripping or breaking, especially in older cars. If a gear is stripped, the motor can still run, making the clicking sound, but won't be able to turn the window.
* Wiring/Connector: While less likely, a loose or corroded wire in the harness leading to the window regulator motor can also cause a clicking sound. The intermittent nature of the problem (only when you try to lower the window) makes this less probable, but still possible.
* Fuse (Less Likely): A blown fuse would prevent the motor from running altogether, usually resulting in no response at all, rather than a clicking sound.
Troubleshooting Steps:
1. Check the Fuse: Locate the fuse for the power windows in your fuse box and verify it's not blown. Replace it if it is. However, a blown fuse wouldn't explain the clicking.
2. Listen Carefully: Try to pinpoint the exact location of the clicking. Is it definitely under the dash, or could it be closer to the door? This will help narrow down the source.
3. Manual Check (If Possible): If you can safely access the window regulator mechanism (may require partial disassembly of the door panel), try manually operating the regulator arm to see if it's binding or seized.
4. Inspect Wiring: If you're comfortable working with car electronics, inspect the wiring harness connecting to the window regulator motor for any damage or corrosion.
Most Likely Solution:
The most probable fix is replacing the entire window regulator. These are relatively inexpensive parts and can be found online or at auto parts stores. Replacing it is a moderately involved job requiring removal of the door panel and some careful disassembly, so if you're not comfortable with auto repair, it's best to take it to a mechanic.
