Have a 2008 Prius still under warranty. Can't find anything wrong except for the rear window defogger. In the 5 months I have owned the car I only needed the defogger two times and it did not work either time. After a half hour driving with the defogger on there was only about 1/8 inch of window defogged at each wire. The dealer "checked" it and said it checks out but bring it it next time it is happening. It obviously impossible because it happens so infrequently and both times at night. Has anyone else had a bad rear window defogger? Any suggestions on getting the dealer to do more than look at it and say it checks out?
You can also set a couple of bags of ice on the rear window. Once it gets good and cold, pull off the ice and it should fog up nicely, assuming some humidity. Tom
The suggestion to cool the hatch with ice and then check for defogging action is reasonable. Further, if you have access to a voltmeter, see if you can measure ~14V when measuring across both ends of the defrost element. My guess is that this voltage will not be present, and if not, this is evidence of a problem. This would indicate that either the wiring harness, the relay, or the fuse is bad.
Thanks for the suggestions. I have multimeter and would like to check whether the element is getting voltage. It might also be possible to disconnect the defogger and do a continuity check for a broken element. The problem: Where are the connectors from the defogger to the car wiring located? On my last car they were right on the rear window but in the Prius they are concealed somewhere. I thought about doing it through the fuse connectors but the fuse box is near inaccessable.
The defroster wiring is hidden by the hatch trim. However, you may be able to measure the voltage directly on the defroster elements, and if so you should be able to read 14V from one side to the other when the car is READY and the rear defroster is turned on. Just be careful not to scratch the element, causing an open circuit. One way to protect the defroster element would be to use a small piece of aluminum foil between the element and your multimeter probe.
Was your brief defogger use for exterior ice removal or interior "fog" moisture? It's more effective for ice melting on exterior, more than fog removal on interior. Use of A/C defog mode works best for interior moisture, even in the back.
I would have thought the window elements would be electrically insulated? But I'll give it a try with the aluminum foil to avoid any element damage. The defogger was used to remove inside fog...not outside frost. The next time it happens I'll run the front window defogger full blast and see if it works. Thanks for all the tips.
