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  1. #1
    Established Member Two Rings
    Join Date
    Sep 01 2007
    AZ Member #
    20738
    My Garage
    90 Eclipse GSX. 04 A6 4.2l
    Location
    W. Mass.

    How do heated mirrors work?

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    I know theres an heater element in them that warms them up. I'm more concerned with how they operate.

    In my 80 quattro, the mirrors would warm up when I turned the rear defroster on. Not the case with my 96 a4. Do they work by temperature? I don't see any other switch that would activate them.

    Now I've read about the "browning" which is caused by the heating element expiring. Would that cause the element to stop working? Both my mirrors have a bit of browning around the edges, which doesn't bother me much, but if that's causing them not to warm up, then I'll be bothered.

  2. #2
    Forum Moderator Four Rings blacka4's Avatar
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    Feb 11 2004
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    43
    My Garage
    Dodge RAM 1500 2008 HD FXDSE2
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    Pittsburgh Area
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    they should work with the rear deforster. or at least that is how my 99.5 worked. if they are not working then I think you might have a problem. I know I had some major browning issues with mine and they continued to work even though the heater was coming off the glass.
    -Rob - Moderator - PM Me!

    RIP:1999.5 Audi A4 1.8TQ Tip Brillant Black
    2009 Dodge RAM 1500 Crew Cab Sport - AZ Plate Frame - Bone Stock otherwise
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  3. #3
    Established Member Two Rings
    Join Date
    Sep 01 2007
    AZ Member #
    20738
    My Garage
    90 Eclipse GSX. 04 A6 4.2l
    Location
    W. Mass.

    So what does audizine recommend? Fuse? Common problem?

  4. #4
    Veteran Member Four Rings walky_talky20's Avatar
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    Jun 30 2008
    AZ Member #
    30427
    Location
    Erie, Pennsylvania

    I was curious about this as well. I just looked at the diagram. It would appear that the mirror heater elements are power *at all times*. I fully expected them to be powered via the rear defroster switch, but that is not the case. They have constant ground and get power through the load reduction relay (so powered whenever the key is in the ON position). Very surprising.

    Knowing this, I may now decide to put a switch in line. I thought the unnecessary heat cycling may cause premature failure of the very expensive Auto-Dimming glass.

    EDIT: Upon closer inspection, it appears the very early B5 A4's did indeed use the rear defogger switch to control them. The switch itself appears to have an internal fuse or breaker just for the mirrors. It looks like it went to the "always on" mirror heating for the 1997 model year. Although it shows the defogger switch for that year was still capable of controlling them (via pin 3), it just wasn't used.
    Last edited by walky_talky20; 10-05-2010 at 08:51 PM.

  5. #5
    Veteran Member Four Rings J Ozzie's Avatar
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    Jun 06 2008
    AZ Member #
    29617
    Location
    Port Moody, Canada

    they work when the Snowflake comes on when it gets cold in the mornings and such! So helpful for warming up your hands too hahah.
    Jamie
    2001 Audi A4
    Vancouver Audi Club.ca

    where's our resident intoxicated lobster Canadian - Thomas

  6. #6
    Veteran Member Four Rings 99blueb5's Avatar
    Join Date
    Mar 10 2008
    AZ Member #
    26268
    My Garage
    01 S4, 99 A4
    Location
    Bellevue, WA

    pretty sure there was also an option for heated mirrors also so not every a4 had them
    99 A4 1.8TQM:
    APR Stage 3 GT28rs kit, CM FX400 6puck, 3" downpipe, Nuespeed catback,Nuespeed short shift, Cxracing fmic, Forge007 DV, H&R coilovers, APR snub mount, gasket ported head, VDO guages, e codes, 6k's, Fiberimages CF hood/trunk, A8 BBK, IE Rods

    00 B5 S4
    Vast stage 3, Rs4 airbox, ko4's,borla cat back, neuspeed sways, statis coils, jhm fmic, SSAC Dp's

  7. #7
    Senior Member Three Rings
    Join Date
    Jul 01 2008
    AZ Member #
    30460
    Location
    Minnesota

    I read somewhere (I think it was the owners manual), and the writeup for the heated mirrors with rear defogger switch mod, that the mirrors are automatically heated depending on the temperature (maybe they are individually controlled at the mirror, and thats why there is always power running to them based on what walky said?).
    Pre-99 1.8

  8. #8
    Established Member Two Rings
    Join Date
    Sep 01 2007
    AZ Member #
    20738
    My Garage
    90 Eclipse GSX. 04 A6 4.2l
    Location
    W. Mass.

    Ok so either the mirrors work via temperature, or via rear defrost switch or they're always on.... Anyone got a definative answer?

    I am going to pull the rear defrost switch tomorrow and see if there indeed is a fuse in it.

  9. #9
    Senior Member Two Rings frameshift18's Avatar
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    Oct 15 2009
    AZ Member #
    49278
    Location
    NE, Ohio
    Items for Sale

    If you really want you could check the voltage of the two wires that plug into the mirror. Check it with the defroster on/off, and with fuse in/out.
    99 A4 1.8tqm

  10. #10
    Veteran Member Four Rings walky_talky20's Avatar
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    Jun 30 2008
    AZ Member #
    30427
    Location
    Erie, Pennsylvania

    Please note that I said the switch "appears" to have an internal fuse. That is just what my diagram shows. It could be a breaker or a surface mount fuse (ie: not replaceable and not visible). I have no idea. This heated mirror business is new to me - it is the first time I've looked into it.

    I also read the manual, and just assumed there was indeed some temperature control. It never occurred to me *what* was actually doing the temp control. Which is odd, I usually want to know how *everything* works on my B5, lol.

    If anybody wants the diagrams I'd be happy to share.

  11. #11
    Active Member One Ring
    Join Date
    Nov 23 2005
    AZ Member #
    8931
    Location
    Woodbury, CT

    I believe there is a thermostat mounted to the back of the mirror glass.

    It should be wired in series with the heater element. At least this is what I remember seeing when I replaced one of mine.
    99.5 1.8TQ



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