omarcarbomb

I have now run down all of the know problems on this new 2000 A8.
Except......

Low B+ voltage problems including not charging battery and car needing jump.

Measured 13.8 at alternator running and 12.5 at battery not running.

Using the climate UP ARROW - RECIRC button codes and selecting 36.
I see at best 13.3v and worst 11.9v

I think car has bad ground somewhere causing voltage drop.

Wanted to know what volatge reading others with no voltage problems see on #36 while driving?

bonus question: what is your idle current at battery pos when car is sleeping for hours. I see 100ma+

silverd2

I've found that the CC code #36 reading is tapped at a point away from the alternator, where it apparently already has a drain on it. On my car, that reading is always a few 10th below the actual voltage getting to my battery from the alternator...so not dependable reading for peak voltage.

The only dependable reading is at the battery with the engine running...it should be exactly what you read right at the alternator, 13.8V would be plenty to keep battery charged...anything above 13.5 would be fine. With everything "perfect", engine running and no drain ( ac off, no lights on, etc) you could get 14-14.1V, but less is still plenty to keep the battery up.

If you have less at the battery than you have at the alternator, I'd start by checking the terminal in the passengers side fender well (behind insert). If you have good voltage at the battery while running, but have trouble starting the car, I look at the battery. A battery can "look" fine (show over 12v with engine off), but fail under load.

omarcarbomb

Thanks

I definetly have voltage drop as I move away from alternator. Already .3v down at that junction under passenger.

Is there a good list/diagram of all of the Power/GND points so I can run them all down. I hear there is one near battery as well.

TSHong

You have to look at Battery voltage and the amps output at the same time. An alternator putting out 5amps, not much will run around 14.4 volts. Now if your alternator is putting out max amps 80 or above, the voltage will drop down to 13.5 volts. They go hand in hand.

silverd2

The battery ground is right next to the battery, under the tail light. But if you're detecting a drop in voltage compared to the reading on the alternator, I'd start at the alternator and work my way back...possibly clean the leads on the alternator, then on to the wheel well junction.

Did you get the .3V drop on the alternator side of the junction? If so, check the connections on the alt...if on the other side of the junction, disconnect and clean it...and so on.

LiranHershman

Two times i have faced voltage drop and both times i called electrician miami to check the issue and fix it.