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.
I had a Honda Odyssey do this for years. Finally took to Battery Plus. They checked my battery at the time (which was not having issues…yet) which they said was good. On a lark i asked if their device could tell if the alternator was okay. He said yes, did something on the meter, and then showed me on the screen the alternator showed “errors”. I had the alternator replaced and the dead batteries stopped happening.
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).
In my experience, it’s most likely the alternator, I’ve replaced so many I’ve lost count.
My local mechanic put a new alternator in my older Accord late last year. It was around $550, including a new serpentine belt.
Honda OEM alternator
I replaced the battery, and upgraded to an AGM battery while I was at it. The problem still wasn’t solved though.
My light was due to alternator-08 odyssey- alternator also was starting to wine pretty bad as well. Local mechanic fixed mine for just over $500 I also had the oil leak happening prior to alternator going bad.
Alternator and the battery are overpriced 2x (google replacement Varta battery and smth like Bosch alternator for your car on pkwteile or idealo).
I bought a brand new, OEM Bosch alternator from Rock Auto. A week back I started noticing a bearing squeak sound in the engine on startup... Later got another battery light... Today was driving and lost power steering suddenly and got battery light again. Pulled over as the car was getting hot quickly. Opened the hood and the serpentine belt was shredded. Alternator was completely seized and had burnt belt on the pulley. Got it towed home.
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