Question about 1999 Audi A4

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The car was connected to jumper cables the wrong way

After the car was jumped with the positve connected to the negitive and the negitive to the postive, the car will not communicate with diagnostic scan tools. the car runs but very poorly like its in failsafe mode.
what control module controls communication with the diagnostic port?
1999 audi A4 1.8L
were can I find used control modules for this car?

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  • emilyandanto Nov 19, 2008

    Thanks for your input guys but my question was not really answered, I was hoping someone might know what control module in the car is in charge with communicating with the obd2 port, is it the ECU?
    I was also hoping to find some info on locating a used ECU to try installing.  The Battery was replaced after the car was jumped.

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The problem is likely the fuse on the back of the stock radio. The VAG tool communicates through the radio, believe it or not. Your radio should also be dead after the reversed battery jump. If this is the case, pull it out of the dash and there's a 7.5 amp brown fuse alongside the cable harness on the back corner. Replace this and see if the problem is fixed.

Posted on Jan 24, 2010

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I'm surprised that you haven't had problems with a dead battery yet. Reversing the polarity at the battery not only doesn't do the battery much good but also will kill the alternator. I would have that checked.
The car's computer may have some internal protection against having the wrong polarity applied to its power inputs but the kind generally used is limited to short-term misapplication and probably failed in seconds, leaving the computer open to random damage.
This could prove to be an expensive repair to get the car back to being whole again.     

Posted on Nov 18, 2008

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Before going any further I would see and automotive electronics expert.

Posted on Nov 18, 2008

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