Rear defogger not working

[Bas]

The rear window defogger in my 2004 Aveo isn't working. It's not a couple of interrupted lines: the entire window stays fogged up. I checked the fuse, but it's still okay. The service manual isn't very helpful, simply stating that I should have it checked by an expert.

Anyone know of any common problems with the rear window defogger, or sugestions for a fix?

[photonut13]

My first suggestion would be to check if you are in fact getting power to the rear window or now. You should be able to unplug the connector on the glass and use a multimeter to find that out.

Then you at least know if you need a new back window or if there is something wrong with the circuit.

[Bas]

I measured the exposed metal bits on either side of the rear window with the multimeter. I first tried a continuity check with the ignition off, and the multimeter beeped so the tracks in the window should be fine. I then switched the ignition on and turned on the rear window defogger, and measured the voltage by touching the terminals to the metal connector bits on either side, getting a measurement of 12 volts. Weirdly, if I do a continuity check when the defogger is on, the multimeter doesn't beep; when the defogger is off, it does.

So, two mysteries. Why is the continuity broken (yet 12V being measured) when the defogger is on, and if the defogger is getting 12V of power, why isn't it defogging the window? Any ideas?

[photonut13]

The only thing I can think of is that while current may still be able to pass through one path, that doesn't mean that the tracks are still functional as a heater.

The part about not having continuity when it is on is really puzzling, I don't know what to make of that.....

I see two possibilities:

1) Something really weird is wrong with the tracks, you will have to replace the window.

2) Maybe there is something wrong with the ground lead? While you could test it with a multimeter, but it won't tell you if the ground is flaky or marginal for sure, you could try running an alternate ground temporarily to see if that makes it work, but if that still does not make it defog, then we return to option 1.

[Bas]

Well, closer inspection (and in daylight) revealed the obvious problem: the entire grid is gone. What I thought was the grid was just regular, non-conductive yellow paint inside (?) the glass: the actual conductive lines were pretty much all gone. I found some remainders near the edges - they peel off as soon as you look at them. It looks like the previous owner scraped the inside of the window, or something. Weird.

Anyway, that solves that mystery. Now I'm wondering: if I get a couple of those repair kits, some tape and a lot of patience, would it be possible to just repaint the grid with that repair stuff? Spending a couple bucks and an hour or two on a few of those kits beats paying a couple hundred on a new window...

[amoretto]

I just realized I recently had to replace rear window and first winter came and I see defrost doesn't work. It was a cheap window, not an original. Only highest and lowest lines of the grid work. Any ideas?