* Window Regulator: This is the most common cause. The regulator is the mechanical part that moves the window up and down. Over time, the gears can strip, the motor can weaken, or the cables can break. Since it works from both switches, it suggests the motor still has power, but the mechanical components are failing to provide consistent upward motion.
* Window Motor: While less likely than the regulator, the motor itself could be failing. It might have enough strength to raise the window from a direct power source (like the switch), but not enough to consistently overcome friction in the regulator.
* Window Switch (Passenger Side): Although the window works from both switches, a faulty passenger-side switch could be contributing to the inconsistent operation. A dirty or partially failing switch might send intermittent signals, leading to the window not always going all the way up.
* Wiring Harness (within the door): The wiring harness running within the door to the window motor and regulator is prone to damage from flexing and wear. A pinched or damaged wire could cause intermittent problems. This is more likely if the problem is intermittent and only sometimes occurs.
* Power Supply Issues (Less Likely): While less probable given that it works from both switches, a weak battery or a problem with the power supply to the window system could still contribute.
Troubleshooting Steps:
1. Inspect the Window Regulator: If you're comfortable with some car repair, remove the door panel (plenty of online tutorials for this) and visually inspect the window regulator. Look for broken cables, stripped gears, or any other obvious damage. This is the most likely solution.
2. Test the Passenger-Side Switch: If the regulator looks okay, try swapping the passenger and driver's side switches. If the problem follows the switch, you've identified the faulty part.
3. Check the Wiring Harness: Again, with the door panel off, carefully examine the wiring harness for any cuts, frays, or loose connections.
4. Battery Voltage Test (Least Likely): Check the battery voltage to rule out power supply problems.
If you're not comfortable working on car repairs, take your vehicle to a mechanic. They can diagnose the problem efficiently and accurately. Describing the symptom (works from both switches, but doesn't always go all the way up) will help them quickly pinpoint the issue.
