Bosch Alternators have 2 posts on them, the big one is for main battery ground, the smaller one is for the exciter or blue wire. When the cars ignition switch is turned on, the Dash light (led and diode) applies 12V+ to the coils to excite them, so the alternator can produce a charge. When the Alternator is producing current and voltage it goes to 13.5-14Volts.
The part # for the Alternator (Automatic trans) is 6H903016L and it's made by Bosh. [Europaparts](https://parts.audiusa.com/p/Audi_2012_A4-Base-Sedan-20L-AT-Quattro/Alternator/48001649/06H903016L.html) sell's it for $499.95 (OEM).
I changed out my original Valeo alternator with a Bosch unit at 100k miles. Never had a problem with either one.
I bought a Bosch reman for my X5 about 3 years ago, no issues whatsoever.
Please, genuine alternators are only like $30 more and you won't suffer these issues. And also they last.
I'm guessing you could be Australian the labour charge would be somewhere between 120 and 150 per hour plus parts which retail close to 550 for a good quality Bosch unit so your not too far off the mark with the quote.
I order a Bosch AL113MX Reman Alternator (yep Bosch reman the Motorola) since that was what was currently in there. The 81 has a big square York compressor mounted right on top of the alternator which means that to get the rear alternator bolt you better have the right extensions and you are going to do it blind. So after at lot of effort I got the old alternator out and the new one in and only then did I notice that the pulley did not line up.
13V is normal for a stock Bosch alternator. There are 14V or adjustable voltage regulator available as a replacement.
Have been burned by aftermarket alternators. I'll spend the money for an OEM every time.
Ive had a few Bosch reman failures lately at my shop as well, although they were for N52s, all bearing noise after about a year.
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