The windshield wipers on my 2007 Jeep Wrangler started having problems several months back. At first they would randomly not find home and cycle an extra time or two before they finally stopped. Eventually the home position ended up a few inches up on the windshield instead of at the bottom. Then intermittent on the wiper settings yielded two wipes, then pause. Four wipes, then pause. Seven wipes, then pause etc, etc. Finally intermittent settings yielded continual wiping as if it were on low speed setting. A single wipe command would cause the wiper to stop whenever you released the stalk on the steering column. You had to manually home it or turn the wipers on to get it near home position.
I've worked on electronics involving encoder wheels and sensor flags to indicate "home" positions much like a crank or cam position sensor works, so I figured it was a flag or mechanism of some sort that wasn't working properly. Tonight I removed the wiper motor to see if I could fix the problem. The problem ended up being grease from the worm gear mechanism contaminating some contact fingers.
This takes 30-45 minutes and only requires a few torx bits, a couple sockets, a flathead screwdriver and something to clean up the grease with.
Use you fingers to lift the plastic cap covering the nut securing the wiper arms to the splined studs on the wiping mechanism. Spreading the plastic outwards on the sides allows it to easily pivot up. Remove the 13mm nut holding the wiper arm on the splined stud. Now pivot the wiper arm vertical, and lift it off the splined stud.
Remove four torx screws holding the cowl down, and then use a large flathead screwdriver to pry up and out the two plastic fasteners securing the screen under the hood. A trim panel tool you can get at Autozone or Advanced will make this easier. Lift the cowl up and then forward to release two plastic feet near the bottom of the windshield. Rotate the back end up and lift off the cowl and plastic screen. Lowering the hood will make this step easier, but it is not necessary.
Disconnect the wiring to the wiper motor by releasing the red plastic lock tab, pressing the catch and pulling. Remove two 10mm bolts holding the wiper assembly to the jeep. Lift the wiper assembly up and out of the cowl area. Note the rubber foot sitting in a hole under the motor.
Remove three torx screws holding down the cover on the gears and position indication portion of the motor. Remove the black plastic cover by releasing two plastic catches on the cover. Careful, they are likely brittle and might break.
More views of the wiper motor assembly:
After lifting off the cover you will see how the grease from the worm gear mechanism has contaminated the copper spring fingers which allow the jeeps electronic control module [ECM] to determine wiper arm position.
Clean the face of the metal/plastic disk and the contact fingers. Reassemble in reverse order and the ECM should be able to find home again (for a while).