The windshield wipers on my '05 Terraza van did not work, so took it to the dealership - their diagnostic test showed nothing wrong with the motor and nothing wrong with the switch. The serviceman showed me that they worked - for him. Later that day, I tried them and they did not work. Since then I have discovered that if the switch is on when I start the engine, they will go back and forth a few times, then quit. I cannot get them to start when I am driving, so therefore do not drive it very far if there is any chance of rain. What do I do?
Intermittent problems can be hard to pin down. I would try to find out if the problem is due to a problem with the power to the motor. It would be good to know which wire to check going to the motor carriies the power to it. Checking the voltage on wire when the trouble is occuring would tell you the story.
In other makes problems like this were found to be caused by the module that permits intermittent function (variable speed)
In some vehicles, the lead to the wiper motor is the positive lead and is always hot. The switch completes the circuit to the chassis. One possibility is that the ground from the switch is bad.