I know I saw this subject questioned over on hybridcars.com - but I couldn't find it, and I never saw it resolved anyway.
Just having a near blizzard yesterday,(18deg snowing & 40mph winds) this is the first time I've noticed-
started the car up to warm up for a minute (I know - I never do this- it was just miserable out & the glass was all iced up) while I scraped the windshield & rear glass. I pretty much never use defrost (except for fogging) and always scrape my glass clean. rear defroster is not on, heater/ventilation dash dial is set to face & foot, and NOT ON. rear defrost button is also NOT ON. so I scrape the windsheild, go to the back and the rear glass is melting on the defroster wires - nothing is on, but the defroster has activated!
So what's the deal with this? Is it an automatic temperature thing that there is no manual control over? Is it on all the time- even in summer? anybody know?
and yeah.... my average went down 2mpg from idleing & driving a short way through slush to pick up the kid & french horn.

 

So are you saying that the heat wasn't on at all?

If it was I would suggest that maybe the wire for the defroster heated up faster than the glass and/or held heat better so the heat was transfering at that point more than other points.

 

I doubt it would be that tbaleno. In the time it takes to scrape the front windsheild the car wouldnt have heated up enough to melt ice. That is a curious situation though...i look forward to the answer.

 

yeah-
NOTHING (other than the engine was started) was on: no heat, no defroster- **** was not even set to defrost.
whadaya think????

 

In the brouchure for the Honda Civic Hybrid it notes the following feature:
I don't know exactly what that means.
If you have your Civic Owners manual, is there anything in it about the defroster automatically being on for "x" minutes if the temperature is below "x" degrees?
(I'm going to check my Insight manual to see if it has a similar feature.)

 

If you press the defroster button it will turn off by itself after x amount of minutes.

As far as I know you have to press the button to turn it on.

 

I did look in the manual - it only mentions the rear defrost button- which, when pushed in (it wasn't) lights up and does have an automatic shutoff after 15minutes. the only other defrost feature is the climate control/dashboard **** which defrosts the windsheild- and I don't have defrost even selected so that autostop will engage.

So nothing in the manual about automatic defrost if the temps are too low- and you can only tell if there's ice or snow on the rear glass, which is why I only noticed it last storm.
So if the defrost button isn't on, why is the rear defroster working? anybody else in the northern/ winter states noticing this?

 

I think that was me that asked about it on HybridCars.com. Mine still does it. Still get better milage than my other cars, so I can't complain.

 

Hey Steve-
where are you driving and have you noticed any pattern to it? I only saw it that one time and it's warming up here in ny so if it's (hopefuly) temp triggered I won't see it till next winter.
the other day I got in the car and looked in the rear view mirror. my daughter (13)says "look mom, the rear defroster is doing it again!"
-she had taken her finger and traced the wires in the exterior condensation.

sure would like to know what the deal is.
I'm happy though - just got 51mpg both ways to grandma's house for easter (300m)with 2 adults, 2 kids, and a trunk full of chocolate eggs.

 

I live near DC. I can't say as it's a regular thing or temperature controlled. I don't think it did it today and it was raining.

One day we'll probbaly get a recall for it.