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Thread: Golf MK7 Electric Auxillary Heater, possible fault

  1. #11
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    I'm not familiar with latest model years heating system typical faults yet, but I have troubleshooted and repaired a lot of VAG cars. Main principles and logic should be the same. ECU is not allowing switch on electrical additional heater in full power mode, if it "see" alternator is overloaded.
    In temperatures below 0 degrees C all processes happens slower - glow plugs are heated for longer time, starter is cranked a bit longer - means more energy drawn from battery. Battery is not accumulating energy back so quickly, too. People are switching on heater to full power/full speed of heater fan + window and mirror defrosters. That all electrical consumers switched on in total takes so much power that alternator may be already working on the edge of overload. Earlier production alternators sends load information to ECU via DF signal, latest ones communicate via LIN providing ECU a lot of information about alternator state.
    A lot of things depends how software of each particular module is written. I guess, recharging battery back to normal charge level is priority #1 after engine is started, additional electrical heater should be the very last in that priority list.
    As Your car is under warranty, let's allow VW to solve this. But I'd test this theory by monitoring alternator load in corresponding MVB's and switching powerful electrical consumers (headlights, window heaters, seat heaters etc) off for test

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  3. #12
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    Hi Martinsx,

    All great info there, and a lot of it makes sense to me.

    Since reporting this to the dealer, the temperature has risen to a point where the electric heater command is not sent from the ECU. It's interesting to note that VW can not help any more to solve this until the temperature drops below about 4C, where they can run the heater test through software again. Apparently they have no advice on how they can bypass and fool the car to think the outside ambient temperature is colder in the meantime.

    I guess the mk7 alternators come with more advanced information feeds to the ECU and as you say it is reasonable to assume that the electric heater is put to the back of the list behind headlights, starter etc... We shall see if they come up with a definitive answer but this is not looking promising any time soon.

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  5. #13
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    Is it really hard to figure out that any temperature may be imitated just by connecting potentiometer (variable resistor) in place of outside temperature sensor?
    Looks like a lot of dealers all around the world are able only do step by step troubleshooting procedures as they are prepared in ODIS "guided fault finding" or written in manuals, they forgot to use their brain...

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  7. #14
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    Glad to see Martin got his mojo back /\

    OP there is an additional inline T stat to the heater hoses & that may not be working correctly or are not monitored by the engine controller.

    Maybe investigate them............?
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  8. #15
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    I suggested the variable resistor to the dealer and they came back with the fact it wouldn't be possible as the ecu is receiving temperatures from various sensors before making a decision on whether the electric heater is commanded or not, but I summized that they didn't know how many sensors were being analysed in order for the ECU to make a decision on the heater. I understand what you are saying and if it was out of warranty I would be doing as you suggested.

    Hi Jack, not sure about where to look for the inline heater hose thermostat or how that would affect the command on the electric element. Nonetheless, I have left it with VW for the time being for them to worry about...

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