* Switch Failure: The most likely culprit is a faulty driver's side window switch itself. The portion responsible for lowering the passenger window might be broken internally, while the raising function still works.
* Wiring Issue: A broken or corroded wire in the harness leading to or from the switch could interrupt the signal to lower the passenger window. This is especially true if the wire is flexed frequently as the switch moves.
* Window Regulator Motor (Passenger Side): While the switch controls the motor, a problem with the motor itself (passenger side) could cause it to not respond to the lower command. This is less likely if the passenger window raises correctly.
* Fuse: Less probable but possible, a blown fuse specific to the window motors could be the issue. Check your owner's manual for the correct fuse.
* Master Switch Relay (Rare): In some vehicles, a relay controls power to the window motor circuitry. Failure of this relay (though less common) could be the root cause.
Troubleshooting Steps:
1. Check the Fuse: This is the easiest first step. Locate the appropriate fuse in the fuse box and verify it's not blown.
2. Inspect the Switch: Carefully examine the driver's side window switch. Look for any obvious signs of damage or wear. A visual inspection might not reveal everything, but it's a starting point.
3. Test the Passenger Window Switch Directly: If you have a multimeter, you could test the voltage reaching the passenger window motor when trying to lower it using the driver's side switch. *Caution: Working with car electrics involves risk of injury. If you're not comfortable with this, proceed to step 4.*
4. Check Wiring: Carefully inspect the wiring harness connected to both the driver's side switch and the passenger side motor. Look for broken, frayed, or corroded wires. This often requires removing some interior panels.
5. Test the Passenger Window Motor: With the window down, try manually lifting the passenger window. If it's difficult to lift by hand, the motor itself may be faulty.
Most Likely Solution: Given the described problem (raises but doesn't lower), the driver-side window switch is the most likely culprit. Replacement is often the most straightforward solution.
Remember to consult your vehicle's repair manual for detailed wiring diagrams and specific fuse locations. If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic.
