* Weak Motor: The most common culprit. The motor might be worn out, its brushes are worn, or it's simply struggling with increased resistance. This is especially likely if the window is slow even when it does move.
* Binding Regulator: The window regulator is the mechanism that moves the window up and down. It uses a series of rollers and tracks. If these are bent, broken, or jammed with debris (like dirt, grime, or even a piece of broken glass), the motor will stall as it struggles to overcome the resistance. This is a very common issue.
* Reverse Current Limiter: Some vehicles have a system that stops the motor if it detects excessive current draw (i.e., a significant blockage). A binding regulator or a partially seized motor could trigger this.
* Wiring Issue: A pinched, broken, or corroded wire in the power window circuit can interrupt power, leading to the motor stopping. This is less likely to cause a consistently partial roll-down, but it's possible.
* Switch Problem: Though less common, a faulty window switch could send an intermittent or weak signal, causing the motor to cut out. Try the switch multiple times; if the behavior changes, it might be the switch.
* Overloaded Motor: While it's less likely, too much weight on the window (e.g., something jammed in the track) may be too much for the motor. Check for any obstructions.
Troubleshooting Steps:
1. Inspect the Window Tracks and Regulator: Carefully examine the window tracks for debris, bent parts, or broken rollers. Look for anything that might be binding the window. If you see damage, repair or replacement is likely needed.
2. Listen Carefully: When you try to roll the window down, listen closely. A grinding sound indicates a problem with the regulator. A clicking or buzzing sound might suggest a weak motor or a wiring issue.
3. Check the Switch: Try the window switch multiple times. See if the behavior changes. A faulty switch could intermittently stop the motor. Test with other switches if possible (if your model has more than one for different windows).
4. Test Motor Power: This is more advanced and requires electrical knowledge and tools. You may need to check the voltage at the motor itself to confirm power is getting to the motor.
Likely Solution:
In most cases with this symptom, the problem is either a weak motor or a binding regulator. Unless you're comfortable working on car electrical systems, it's recommended to take it to a mechanic for diagnosis and repair. Replacing the regulator assembly is often the solution, as it is typically more economical than replacing the motor, and both often fail together.
