* Wiper Motor Issues: The most likely culprit is a problem with the wiper motor itself. It might be failing, partially seized, or have internal electrical issues preventing it from powering both wipers. Sometimes, a motor can still function weakly enough to move one arm, but not both.
* Linkage Problem: The mechanism that connects the motor to the wiper arms (the linkage) could be broken, bent, or disconnected on one side. This is relatively common, especially with age and wear. Check for broken or dislodged parts in the linkage system.
* Electrical Issues: A faulty wiper switch, wiring harness damage (especially around the motor and linkage), a blown fuse (check your owner's manual for the wiper fuse), or a relay problem can all cause one wiper to malfunction.
* Parked Incorrectly: Although unlikely, if the wiper arms were parked improperly (not fully seated), they might not operate in tandem.
* Low Wiper Fluid (Less Likely): While a low fluid level won't directly stop a wiper from working, if the system is trying to compensate for a lack of fluid, it might exert uneven pressure on the motor, affecting one arm.
Troubleshooting Steps:
1. Check the Fuses: Locate the fuse for the wipers in your fuse box (consult your owner's manual) and ensure it's not blown. Replace it if necessary.
2. Inspect the Linkage: Visually inspect the linkage connecting the motor to the wiper arms. Look for any broken, bent, or disconnected parts.
3. Test the Wiper Switch: Try using different wiper speeds. If the other wiper works on one speed but not another, the switch itself might be faulty.
4. Listen to the Motor: With the wipers on, listen carefully to the motor. A grinding or unusual noise indicates a potential problem with the motor.
5. Check the Wiring: Carefully examine the wiring harness leading to the wiper motor and linkage for any signs of damage, loose connections, or corrosion.
If you're not comfortable working on your car yourself, it's best to take it to a qualified mechanic for diagnosis and repair. The problem could be simple (like a blown fuse) or more complex (requiring motor or linkage replacement). A mechanic can properly diagnose the issue and give you an accurate repair estimate.
