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Rear Defrost Not Working

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by OneRoad, Oct 23, 2015.

  1. OneRoad

    OneRoad New Member

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    2008 Prius 115,000 miles
    Purchased 2 years ago @ 78,000 miles

    My rear defrost stopped working at some point towards the end of last winter. I recently started to need it again with fall weather in Pennsylvania. I was able to find the fuse for it with the help of other posts here. I replaced it and that did not solve the problem. I took off the trim around the rear hatch window to make sure all the connections were solid and they were. Also the grid seems intact, I don't see any breaks in the defroster lines. The rear view mirror defrosters work whenever I hit the button to turn on the rear defrost.


    At this point I am considering changing the rear defrost relay. I think it is located next to the fuse but I was wondering if anyone could tell me for certain where it is. Any other advice it areas to check is much appreciated. Thanks in advance.
     
    #1 OneRoad, Oct 23, 2015
  2. WilDavis

    WilDavis Senior Member

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    Have you checked/cleaned all the connections? De-frosters can take a fair current, and even slight resistance in a bad or dodgy connection will impair the performance! (…you've tested the fuse, right?) …bad switch? If you have access to a multi-meter (yours or a friend's) check the resistance across the connectors to the grid (when disconnected) - I would guess that it should be around or less than ¼ ohm (guess), or even better, to start with measure the voltage across the grid when it is switched on (should be 12V). If no volts, or low volts, then your problem is up-stream from the connection. - hope this helps - Wil

    Edit: Your hunch about the relay sounds about right, and you might test it as I've described.
     
    #2 WilDavis, Oct 23, 2015
  3. andrewclaus

    andrewclaus Active Member

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    My wiring diagram shows the relay is called "DEF" (same as the 40A fuse), and it looks like it's on the driver's compartment junction block along with the fuse. I have never had to look at mine and my wife has the car out of town so I can't verify. I agree that rather than replacing things and hoping for the best, you might want to check terminal voltages with a multimeter. Good luck.
     
    #3 andrewclaus, Oct 23, 2015
  4. OneRoad

    OneRoad New Member

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    Thank you both for your replies. I do have a multimeter and will test some things out with it like you recommend. My wife has me pretty busy for the rest of the weekend but I'll let you know the results when I get to it.
     
    #4 OneRoad, Oct 24, 2015
  5. ChapmanF

    ChapmanF Senior Member

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    Even if it sets you back $15 at techinfo.toyota.com to get your wiring diagram and the troubleshooting steps from the diagnostics volume of the manual, even if you price yourself at minimum wage you'll probably save a lot more than that, just in the time and misdirected effort you won't have spent on the way to tracking down your problem.

    Good luck!
    -Chap
     
    #5 ChapmanF, Oct 24, 2015
  6. OneRoad

    OneRoad New Member

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    Everything checked out fine with the multimeter. Thanks for your encouragement there.

    We had the windows tinted last winter and the rear window had to be redone. When they did it the old tint was peeled off like a sticker and now I realize that all the conductive material was taken along with it. It was so evenly removed that it was hard to notice.

    I am researching repairs but 2 places have told me that window replacement would be the only option. I went back to the tint shop and they are denying any wrongdoing. No receipt and Cash deal leaves me with no recourse. I think I figured back then that they were just tinting the windows, 'what could go wrong'. Funny think is that he offered to redo the tint for free, which is odd since it's not his fault. One of those live and learn situations I guess.
     
    #6 OneRoad, Oct 29, 2015
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