radhaz

I was driving to work this morning on the freeway when I felt a bang. I looked at the instrument cluster and saw that prnd432 was lit up. No response when put into Tip mode. The car stayed in 5th. I tried to limp it back home, but as I was driving, I saw that the battery was draining rapidly. Eventually, I had no throttle, even though the engine was still idling. I pulled over and walked the 2 miles back to the house and called a tow.
After the car was parked, I turned on the ignition, and saw that the gear indicator was normal. The car started, and I pulled it into the garage. The battery didn't appear to be charging. I measured the battery with the car running and read ~11.5 volts and falling. I hooked it up to the battery charger and the battery is now charging, but the progress is very slow, which might be normal. The battery is what came with the car when I bought it a few years ago.
If I let it charge and it doesn't reach 100% (according to the microprocessor controlled charger) I will assume the battery needs to be replaced. Is there any chance that the alternator might be good in this case? I'm not looking forward to yanking the nose off the car.

SloopJohnB@mac.com

Battery should be checked with load tester. Charge the battery for 24 hours and load test it. If you don't have one, buy or borrow one.

The alternator should be able to keep the car running with a low or dying battery..the problem is starting the car.

If you don't have 14+ volts at the battery with the car running the alternator is almost certainly the problem, but I wonder if ¥ou just didn't blow the serpentine belt...how was your engine and oil temperature.

AS for yanking the nose, you may be able to get the alternator off through the top if you remove the right front headlight (and the air intake/air filter stuff above it). That's the trick I use on a 4.2 to get the GD oil cooler out...and to replace that front engine mount. If you have a 4.2 you might want to check that front mount and the oil cooler tube while you have the alternator out.

If it's just the serpentine belt, replace the belt and the tensioner (if car has over 100K on it) and then check the alternator output.

SloopJohnB@mac.com

Bang? Did the serpentine belt break?

radhaz

Thanks for the reply.
The bang I felt made the car jerk. I've looked at the belt, running and not running, and it appears to be intact and in good condition. It was changed 20k ago with the timing belt. I don't hear any strange sounds from the alternator.
I put a good charge on the battery, and it cranks the car well. I guess I'm doing the alternator.
Is there a way to check the charging system with my Vag-Com?

sqplus

year, motor? You're assumptions are close but unfortunately the alternator is probably toast if you have a C5 with the original part. My OEM alt lasted about 9 years, and IIRC 110k miles. the battery could be fine, just needs a recharge.

In theory, if your battery died while driving and the alt WAS working you would still be able to drive it home no problem and the next time you tried to start the car it would not.

First things first if your battery is dead/dying is to disconnect the vehicle power cables, pull the battery from the vehicle and charge it until full. Also, check the water level in the battery before If it is really dead this could take awhile depending on your charger 12-24 hours sometimes more. It sounds like you probably know this but to cover all the bases, the battery should read 12.5v when charged and not in the vehicle.

Reinstall the battery and start the car, once it idles down it should read between 13.8v and 14.4v with no accessories on. If you read anything less than this at the battery then the alternator is not charging the battery properly. You could also use the vagcom, if you have one, to get the system voltage.

The alt. IS quite a PITA but easier than the timing belt job! I just did the alt last year so if you need any help/pointers just let me know. Keep us posted!

radhaz

The car is a '01 A6 2.8, the one in my avatar. It recently went over 100k, so you're right, it was probably due to go.
What is puzzling me is why there was no indication that the battery was draining. Isn't there a beep when that happens? I didn't notice the battery light until I saw the voltage dropping. The gear indicator and trans not shifting is strange also. Maybe solar flares~

sqplus

Yeah, mine went the same way, got in started up everything worked fine then I noticed the battery light and my voltage guage read 12.x. There isn't really any warning with the alternator, it just stops working one day...although the solar flares probably don't help.

One thing, make sure to check, I believe all of the '01s were the same oem alt but for my 99 there was a split between using Valeo and Bosch built alt. You may want to check that before you buy, and be prepared to spend over $200 depending on where you get it from. Audi wants $650.

sqplus

I'm wondering on the shifting issue if when the system voltage got to a certain point the tip module didn't have enough power to function and shut down...the tranny wouldn't now what to do with no tip controls. Hmmm...

radhaz

Here's the codes from right after the car was dropped off. B+ is the alternator output, right?



Friday,25,June,2010,10:40:26:00107
VCDS Version: Release 908.2
Data version: 20100326



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 4B - Audi A6 C5
Scan: 01 02 03 06 08 15 16 17 18 34 35 36 37 45 55 56 57 65 67 75
76 77

VIN: WAULHxxx
-------------------------------------------------------------------------------
Address 01: Engine Labels: 078-907-551-ATQ.lbl
Part No: 3B0 907 551 BS
Component: 2.8L V6/5V G 0001
Coding: 07251
Shop #: WSC xxxxx
WAULHxxx AUZ7xxx

6 Faults Found:
16804 - Catalyst System; Bank 1: Efficiency Below Threshold
P0420 - 35-10 - - - Intermittent
16814 - Catalyst System; Bank 2: Efficiency Below Threshold
P0430 - 35-00 - -
16946 - System Voltage: Too Low
P0562 - 35-10 - - - Intermittent
17930 - Camshaft Adjustment; Bank 2: Malfunction
P1522 - 35-10 - - - Intermittent
17927 - Camshaft Adjustment; Bank 1: Malfunction
P1519 - 35-10 - - - Intermittent
16891 - Idle Control System RPM: Higher than Expected.
P0507 - 35-00 - -
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 02: Auto Trans Labels: 01V-927-156.lbl
Part No: 4B0 927 156 AK
Component: AG5 01V 2.8l5V USA 3132
Coding: 00002
Shop #: WSC 00000

1 Fault Found:
18159 - Supply Voltage: too High
P1751 - 35-10 - - - Intermittent

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8E0-614-111-EDS.lbl
Part No: 8E0 614 111 A
Component: ABS/EDS 5.3 QUATTRO D10
Shop #: BB 24334

1 Fault Found:
00532 - Supply Voltage B+
07-10 - Signal too Low - Intermittent

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: 4B0-820-043-MY1.lbl
Part No: 4B0 820 043 AG
Component: A6-Klimavollautomat D65
Coding: 00160
Shop #: WSC 02325

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 4B0-959-655-AI8.lbl
Part No: 4B0 959 655 F
Component: Airbag Front+Kopf 2002
Coding: 00307
Shop #: WSC 02325

1 Fault Found:
00532 - Supply Voltage B+
07-10 - Signal too Low - Intermittent

-------------------------------------------------------------------------------
Address 17: Instruments Labels: 4B0-920-xxx-17.lbl
Part No: 4B0 920 981 F
Component: C5-KOMBIINSTR. VDO D12
Coding: 02262
Shop #: WSC 22133
WAULH64B41N143300 AUZ7Z0A1814326

No fault code found.

-------------------------------------------------------------------------------
Address 35: Centr. Locks Labels:
Part No: 4B0 962 258 J


-------------------------------------------------------------------------------
Address 45: Inter. Monitor Labels: None
Part No: 4B0 951 178 A
Component: Innenraumueberw. D04
Coding: 00102
Shop #: WSC 02325

2 Faults Found:
01350 - Alarm via Theft Warning System; Rear
35-00 - -
01462 - Anti-theft alarm ultra sonic Sensor (G209)
53-10 - Supply Voltage Too Low - Intermittent

-------------------------------------------------------------------------------
Address 56: Radio Labels: 8D0-035-1xx-56.lbl
Part No: 4B0 035 195 A
Component: Radio D00
Coding: 00204
Shop #: WSC 02325

No fault code found.

End ---------------------------------------------------------------------

sqplus

IIRC that means Battery positive, also evidenced by 'supply voltage too low' codes. Losing power in a car like this could trigger all of those codes, I didn't let the car drain the battery to dead so I didn't get all of these codes, just one or two of the 'supply voltage too low' signals.

Did you get the battery all charged up yesterday?