98Quattro

Ok, so I was scanning the car with my VAG because the airbag light came on. I cleared the code and then saw under engine module that I also had the following code:

Address 01: Engine Labels: 078-907-551-AHA.lbl
Control Module Part Number: 4D0 907 551 AH
Component and/or Version: 2.8L V6/5V MOTR AT D01
Software Coding: 06252
Work Shop Code: WSC 23261
VCID: 6CCACC42361B
1 Fault Found:

18010 - Power Supply Terminal 30: Voltage too Low
P1602 - 35-10 - - - Intermittent

Readiness: 0000 1101

I cleared the code and when I went to start the car it wouldn't turn over. So I jumped the battery and went to autozone where they checked the battery and it was bad. Bought a new one, installed it and the car started fine but the voltage read fine at first on the voltmeter and then dipped with the A/C turned on.....to around 12 volts or sometimes below. I went back and they checked the battery and it checked good.

The car starts fine and drove fine but whenever the A/C is on, and we're in the 100's here, the voltmeter drops to around 12 volts. I scanned the car again and the same fault as well as airbag light.

Is this a bad starter? A bad alternator? the guy at autozone said it failed "low regulator test" but said he couldn't get an amperage reading from the alternator. perhaps he didn't know how to run the test??

Or is this a bad ECU/ECM???

4Driver4

Bad alternator.

98Quattro

Even though I didn't get the "idiot" battery light to stay illuminated on my dash?

69gaugeman

Yes. The light only comes on if there is almost no charging. Sounds like yours has some charging, but likely some damage to the regulator.

SloopJohnB@mac.com

Agreed. Probably a bad VR. A VR is roughly $125, last one I bought dealer had to order it from Texas...LOL. They're not normally stocked; dealer makes his money replacing the entire alternator, probably gets fewer comebacks that way too. If you've got more than 140K miles on the alternator it's time to replace the VR anyway. You can pull the alternator and drop the VR and check the brush length...5mm is the service limit. Short brushes (or a scored slip ring..replace alternator) can give intermittent/low voltage.

Luckily I had the alternator out for a plastic coolant pipe replacement and I could afford the three or four days it took to get the VR in.

You can get a cheap in-car alternator tester from Sun or Actron or whatever (maybe Vag-com would tell you if a diode in the diode bridge was gone) that would tell you if you were getting unrectified AC component which would tend to give you a low DC voltage reading. But before I'd replace an alternator I'd pull it and take the alt to autozone or your parts dealer with an alternator tester...they'll run it up and tell you what exactly is wrong with the alternator. You can spin the armature/rotor yourself and see how it feels..if it's rough or noisy it's generally best to just get a new alternator or rebuilt from a dependable source...I wouldn't use autozone or pepboyz for an audi rebuild.

98Quattro

Well I picked up a rebuilt Bosch alternator from O'Reilly's yesterday and my Indy is going to do the swap for me on Friday. In the meantime, I've left the Audi parked in my garage with the battery disconnected.

Can't wait to have her fixed up on Friday.

audi1031

I am not sure if this will happen but you may need to do a TB sync if you leave it disconnected to long. I did that for a couple hours and had to have a TB reset

98Quattro

What does that mean? Will the engine not run properly after having the battery disconnected for so long?

2.7Lturbo

dont worry, the thottle body will go through its auto adaptation cycle when the power is reconnected, you will hear it wirrr and click

SloopJohnB@mac.com

Should have no problem with installing a new alternator...I left my battery disconnected for almost two weeks and when I put the alternator back in with the new VR and connected up the battery it worked fine.