Rear Wiper Performing Random Acts

[joshespdx]

I'm experiencing an intermittent fault with my rear wiper. Here's how it plays out: I turn on my rear wiper to clear the back window. After it completes it's initial sequence of 3 or 4 wipes I rotate the switch to the "Off" position. At this point the wiper will complete one stroke, go to the full rest position under the window and then start another stroke. Again, it will return to the full rest position under the window and then start again. The wiper is behaving like it is turned on in the continuous operation mode, but returning to the full rest position between strokes. Cycling the switch has no effect. Cycling the windshield wipers up front has no effect. Turning the vehicle completely off and back on doesn't always work. Sometimes when cycling the vehicle power the wiper will stop in the vertical position and then randomly return to the full rest position while I'm driving. It's pretty weird!

Is there a discrete wiper control unit/relay/timing circuit of any kind? Or is it integrated with the wiper motor?

I see a wiper fuse near the driver side kick panel but that seems to be for both front and rear. This isn't behaving like a bad fuse, anyhow.

My next step is to simply check/clean the contacts and re-seat the connector.

Thoughts?

 

[jeremyc74]

There's a control module mounted inside the litigate that handles the wiper functions, but I'd guess your problem is with the switches in the motor. Is there anything stopping the wiper from going all the way down to the home position? Is the arm bent or anything? It sounds to me like it's not seeing "home" and is trying over and over to get there.

 

[TheDurk]

The logic is actually part of the Back Door ECU. The above is a pretty good guess. To confirm, you would test to see if the green/red wire from the wiper motor to the ECU is getting ground when the wiper achieves rest or 'home.' I'd also check the black/white wire for a good ground, and, with any issue in this area, check the wires through the harness between the liftgate and the body for broken insulation, shorts, breaks or other badness. Weird stuff emanates from that spot.

More detail here--I recommend Item 9 in the second link to test motor switches.:

 

[joshespdx]

The logic is actually part of the Back Door ECU. The above is a pretty good guess. To confirm, you would test to see if the green/red wire from the wiper motor to the ECU is getting ground when the wiper achieves rest or 'home.' I'd also check the black/white wire for a good ground, and, with any issue in this area, check the wires through the harness between the liftgate and the body for broken insulation, shorts, breaks or other badness. Weird stuff emanates from that spot.

More detail here--I recommend Item 9 in the second link to test motor switches.:

I'll break out the Fluke 87 this week and get to work on it. Thanks for the schematics! Absolutely what I was hoping to see. I'll report back when I have this solved.

Josh