Today on my way to work it was about 58° out and I decided to turn on my defrosters and about 10 minutes into my drive on the freeway my window randomly shattered. Before this icemelt some sort of burning plastic but thought it was coming from outside but the smell kept getting stronger and then all of a sudden my rear window shattered. No fun at all!

After doing some research on this form I found out that I'm not the first person this has happened to you

I think about this every time I hit that button... I mean, I want a clear rear window to see through but damn, not that clear... sorry to hear that

so whats the cause of it?

as do I.

I don't like that the mirrors are tied into the rear window defroster. sometimes the mirrors are frosted up, but the rear window isn't, or vice versa. id like to be able to control them independently, to hopefully avoid things like this...

Lol, 58 degrees and we are about to turn the a/c on. I never thought of using the rear defroster for fog as I thought it was for snow and ice. Then again, never had an issue with fog on the intetior rear hatch window.

first off sucks to the OP.

and I'm not sure if anyone has figured out why the rear windows are shattering with the defroster on but it sounds like an electrical short of some king as everyone I remember reading has reported melting plastic before it shattered.

Anyone have an educated guesses on why this is happening to 4th gens?

This happened to me not too long ago. Haven't used the defroster since.

• Defect in glass
• Defect in solder
• Excessive corrosion at solder
• Something else?

Happened last week to the guy that owns the tire shop down the road in his 04 SR5. I told him that I have read of this happening to a few other people and he went off the reservation. Pretty sure he is still on the phone with Toyota.

OP. According to the glass guy, the defrosters just heat up too fast and the glass tries to expand where it is warm.

I would think there is no fix for it, as a matter of fear, I never used the rear defrosters in either of my 4th gens.

Still bitter....lol

Will comprehensive cover this?

As an insurance underwriter for a property and casualty insurance company that writes a lot of auto insurance I can safely say that no, comprehensive coverage most likely won't apply to this. Occasionally an insurance company will pay when they don't have to for some reason but I wouldn't count on it.

They pay for chips and cracks to the front windshield because that damage is evidence of a covered event (impact of some sort). Damage to the vehicle from material defect isn't a peril normally covered by an insurance policy.

One fix for it is to install a resistor in the circuit. Downside is this will also slow defrosting time. Take a look at how many watts the heater is sucking up and calculate the ohms required to knock it back maybe 10% using something like Ohm's Law / Watt's Law Calculator

Edit: see post/scematics below - parallel circuit, not series. Resistor wouldn't solve issue which is uneven heating, not too much heat too quickly.

Looking over the service manual I've decided to pull my rear window defogger fuse.
The system seems to be wired in a parallel circuit instead of a series circuit. This will lead to the rear window heating unevenly (if there is a broken wire), which will cause SNAP!...

IF you look over the schematics and troubleshooting guide attached you will likely come to the same conclusion...

So unless you know for a fact all of your rear window defogger lines are intact, I wouldn't use it.

Also I saw there is a 15 minute timeout feature on the defogger if you're brave enough to test that.
It also appears the rear window defogger has a seperate fuse than the mirror defoggers, for those models so equipped.

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