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Heater control unit total failure / threw a wobbler - help!

Discussion in 'A6/S6/Allroad forum (C5 Chassis)' started by Ben jah min, Feb 20, 2014.

  1. Ben jah min

    Ben jah min Member

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    I was driving down the road and smelt a burning smell so i pulled over and turned off the ignition and checked to see if the car was on fire, but all was ok at the time. When i then There was acrid black smoke coming out the heater vents upon turning the ignition back on which stopped shortly after losing the display on the heater control unit and the car completely losing its really typing this in only intends to avoid the swear filter which is only going to annoy you when you notice quite how many words have been replaced in your post so id just give up if i were you.

    When I restarted the car a reel of faults came up but the car still runs fine, not even limp mode. Even the illumination on the unit lights up but no display on the LCD screens.

    The main thing causing an issue is the lack of heater / de mist, making it a nightmare to use. My initial thought was the fan had seized and shorted out the circuit, but that doesn't seem to be the case.

    So far I've checked;

    The fan itself, freely spinning 0 volts at terminals / connector,
    The fuses (2x 30A fuses both ok),
    The clima unit itself - swapped with a replacement item same thing happening


    The other faults that occurred at the same time include;

    Orange oil sensor light on display,

    Outside temp reading -37'c when you turn it on but changes like its a thermistor fault but never positive temp EG -20 when its around 14'c outside,

    Traction control light permanently on.

    Im at my whits end as I've only had the car less than 10 weeks after my B5 got crashed into by some idiot not paying attention. Now it looks like this is a dash out job to try and find the cause of the issue.

    Has anyone had something similar before/ Got pointer to check before i submit to getting an auto electrician to charge me a small fortune?

    Any help would massively get me out of a pickle.

    Cheers

    Ben
     
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  3. Dan95x

    Dan95x Member

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    Hi Ben,

    I have always had much older cars than the C5, and would always start with the obvious 'mechanical' fault finding before, but I have rapidly learnt that it is very useful to get a decent VAGCOM scan sooner rather than later before you start ripping stuff apart! They are fairly complicated beasts electronically compared to anything I have ever had before.

    Whereabouts are you? If you are anywhere near Cardiff I will happily scan for you on my cable? (Would happily do it if you are near the midlands too, but I wont be there for a good couple of weeks, and I suspect you want to sort it out sooner than that!)

    Dan
     
  4. Ben jah min

    Ben jah min Member

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    Nice one dan much appreciated, typically the A6 was meant to be a safe purchase for a family barge, like yourself I'm into older cars (Golf VR6's to be precise) but with the audi you can't even remove bulbs without the car throwing up faults!

    I have had it VAGCOM'D but i don't have the fault codes to hand, typically none of them were heater / AC related and I've misplaced the list with the codes on. Its even more so frustrating as my wife had a baby a week ago today and we can't go anywhere due to the car being freezing cold and no good for baby :(

    Ill have a hunt for the list and get back to you on that, my hunch is a shorted / melted cable as the burning smell was a precursor to the massive fail.

    Im not having much luck with cars lately !

    Thanks for the offer though :)
     
  5. Ben jah min

    Ben jah min Member

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    Ive dug out the fault codes it pulled off, they are as follows;

    18043 - power train data bus missing from message from A/C

    18062 - check etc at instruments

    18265 - Load signal error message from ECU

    00562 - sensor oil level sensor open short to plus

    If thats any help

    Thanks

    Ben.
     
  6. @udi A3

    @udi A3 Site Sponsor
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    IIRC there is a pressure switch on the aircon pipe on these that fails and can cause a short in the loom similar to what you have had. I think you really need to probe the wiring for shorts and find that melted bit of loom that your are likely to have hidden away in there.

    It may be a part of the oil level sender loom as its displaying a short to plus.
     

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