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Top or rear window defroster not working on 2005 Prius

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Marci D., Oct 12, 2024.

  1. Marci D.

    Marci D. Junior Member

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    I have a 2005 Prius that had the top rear windshield replaced about 8 months ago after a rock strike. Everything was working for several weeks after the glass replacement then summer came and I didn't need it.
    Recently I turned the defroster on and found that only the small lower window is defrosting. The main rear glass that had been replaced is no longer defrosting.
    I looked carefully and can see no damage or breaks in the defroster lines. I removed the molding and it appears all the wiring is plugged in. Can anyone point me to where the wiring connects between the top glass of the rear windscreen and the lower glass? Obviously the problem is there but I need to look closer. Any other suggestions would be appreciated!
    (Note: I did call the windshield replacement company - they said it's nothing to do with them. It was tested and working when they left and they won't help.)
     
    #1 Marci D., Oct 12, 2024
  2. pasadena_commut

    pasadena_commut Senior Member

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    If you still have access to the wiring test that the expected voltage is present when the rear defroster is on. The only problem I have ever had with a car rear window defroster was the connector not being tight enough so that it could work itself off the tab from the window over time. Also pull off the connectors and verify that neither the tabs nor the connectors are corroded. If the proper voltage is getting to the tab, and the ground is good, then there must be a break in the conducting line somewhere. Use a voltmeter and probe the trace, it will read 12V (ish) until it is below the break, where it will read 0V. It is possible for a section of trace to be disconnected on both sides, where it will probably read the same as just waving the probe around in the air.

    There are other threads on this topic on this site. For instance:

    Rear Defroster not Working | PriusChat
     
    #2 pasadena_commut, Oct 12, 2024
    Marci D. likes this.
  3. ChapmanF

    ChapmanF Senior Member

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    If I remember right, the pattern of heat traces on the glass is that the traces running across the glass are effectively parallel, between a 12-volt common running up and down the glass on one side and a grounded common running up and down on the other side. (It may be a little weirder near one corner of the glass involving the wiper.)

    That would mean that a break in only one trace would usually take just that one trace out of action. If they're all out of action, I'd expect the problem to be right near the 12-volt or the grounded common.
     
    #3 ChapmanF, Oct 12, 2024
    Marci D. likes this.
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