Other possibilities, though less likely given the symptom, include:
* Worn wiper motor brushes: These can cause intermittent operation or weakness at higher speeds.
* Wiring issues: A short or break in the wiring harness, particularly at the higher speed connections, could prevent them from working.
* Wiper switch: A malfunctioning switch could send only the low-speed signal. This is less common than a resistor problem.
* Fuse: While less likely to cause only the high speeds to fail, a blown fuse could be a simple and cheap thing to check.
Troubleshooting steps:
1. Check the fuse: Consult your owner's manual to locate the wiper motor fuse and check its condition.
2. Inspect the wiper motor resistor: This is often located under the dash, near the wiper motor itself. Look for signs of burning, melting, or obvious damage. Access to it may be tricky depending on your model year, and may require removing some trim panels. This usually needs a detailed wiring diagram for the car for precise location, search the web with your specific model number for this wiring diagram. A visual inspection might not reveal an internal problem, though.
3. Test the wiper motor itself: This is more involved and usually requires multimeter skills to check for appropriate voltages and resistances at the motor.
Recommendation:
Since the wiper motor resistor is the most common cause of this specific problem, it's usually the most efficient place to start. You can purchase a replacement resistor relatively inexpensively. If you're not comfortable working on your car's electrical system, it's best to take it to a mechanic. Replacing the resistor might be relatively easy for a competent DIYer but involves some diagnostic work and can be a bit fiddly.
