1997 E39 528i Heated rear window

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  1. 1997 E39 528i Heated rear window 
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    haitch's Car Details
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    Havent been out in the car for a few days due to cold weather. Did start it yesterday and run Rear screen to thaw out and then switched that off and run demist control on full for a while. All the time the engine was running and no probs. This morning after another horrendous frost drove a couple of miles to shops and noticed my rear screen heater switched of after about 5 mins, I re set it and it did the same again. Could this be a sign of low battery? No warning lights on at all.
     
     

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    In Brief, does anyone please know if the heated rear window switch turns itself off to protect a low battery?
     
     

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    it is set on a timer so that once the window is cleared it will automatically turn off, its not 5 minutes though. the cold weather will be putting a lot of strain on the battery though, especially if it is an old battery. Its possible that the cars brain shuts off non essential electrical components, it certainly does in the newer models.
     
     

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    haitch (20-12-2009)

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    Thanks Deano, I'm aware of the timer and it has worked normally on that usually up to an hour before switching off. The handbook says for example you can use the 'rest' button to get residual heat with the engine switched off but that it won't work unless the battery is fully charged. This lead me to believe the Rear window heater may work in a similar way and wondered if anyone had heard of this. I'm off on a 220 mile round trip on Wed and just want to be sure everything is okay before I go, especially in this awful weather.
     
     

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    Dr of BMW gildersol's Avatar
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    Here you go, hope you can understand it

    Rear window defogger


    Thawing phase
    After terminal 15 new start and after being switched on for the first time, the time interval for the rear window defogger is determined in order to achieve an optimum thawing effect.

    Thawing time at outside temperature > 15 o C = 10 minutes

    Thawing time at outside temperature < 15 o C = 17 minutes

    Undervoltage cutout does not take place during the thawing phase

    After-heating phase
    In order to maintain the battery charge level, once the initial thawing period has elapsed, the rear window defogger can only be activated for 5 minutes every time the button is pressed
     
     

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    haitch (21-12-2009),mikesmith2 (21-12-2009)

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    Quote Originally Posted by gildersol View Post
    Here you go, hope you can understand it

    Rear window defogger


    Thawing phase
    After terminal 15 new start and after being switched on for the first time, the time interval for the rear window defogger is determined in order to achieve an optimum thawing effect.

    Thawing time at outside temperature > 15 o C = 10 minutes

    Thawing time at outside temperature < 15 o C = 17 minutes

    Undervoltage cutout does not take place during the thawing phase

    After-heating phase
    In order to maintain the battery charge level, once the initial thawing period has elapsed, the rear window defogger can only be activated for 5 minutes every time the button is pressed
    Hey cheers gildersol, even though it looks a bit complicated I reckon you have answered the question. It must have been in the 'after heating' stage when I noticed it switching off after 5 mins. I tried it again this morning and it stayed on for what must have been the 17 mins, so looks as though alls okay. We live and learn. Many thanks again. Harry.
     
     

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    gildersol (22-12-2009)

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