Intermittent Battery Light

[Vil_Riker]

The car in question is a 2007 A6 C6 with 250k miles.

I've been experiencing intermittent battery light on the dash. The battery light comes on intermittently. When I drive with the battery light on, the battery level drops... When the battery light is not on, the battery charges.

To test quickly, to see if it's the alternator or the battery, I disconnected the positive battery terminal while the battery light was on. The engine immediately died. I tested it when the light was off and the engine continued so this points to the alternator. This is the normal test I have performed on other cars with good quick diagnostic effect.

Last night the battery was at 100% according to MMI. I started it, no battery light but the battery level showed 10% which points to a bad battery. As I drove, the battery reached 40%. Stopped to fill gas, and when I was pulling out of the gas station and was on a decline, the battery light came on. Quickly drove to a parking lot a mile away as the battery drained down to 10%.

What I have noticed is that if the car is parked on a level ground for a few hours, the battery light is off. If I park with the nose facing down on an incline, or am on an incline facing down, the battery light comes on. Once it's on, it doesn't go away when I am driving on a flat surface.

The battery is 7 years old and I will be replacing it anyway. But with an old battery, the issue should have been consistent, not intermittent.

What do you think?

(posted this in Audizine initially but BITOG is a more active forum)

 

[GON]

I think you may have a alternator that is intermittently failing.

 

[SC Maintenance]

I agree with @GON. Bad alternator, or its internal regulator.

Disconnecting the battery cable while running is a really bad idea BTW - you can get a surge the solid state electronics don't like. You can get away with it 9/10 but that one time is expensive.

I suggest a cigarette plug in voltage gauge - like this -you can easily track it while driving. Well worth the 10 bucks. For example - but there are many out there.

https://www.amazon.com/Jebsens-Char...=d2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWM&th=1

 

[vwmaniaman]

My son just had this on his 2005 Camry. We replaced the brushes and no more problem.

 

[Vil_Riker]

I'm tempted to go the cheap route of rebuilding it myself but I think it's a PITA removing the alternator if it doesn't work. A Bosch USA made unit is $275 (plus $100 core) and Poland made Valeo is $375 (no core). I think I'll get the Bosch.

 

[f355spider]

I'm tempted to go the cheap route of rebuilding it myself but I think it's a PITA removing the alternator if it doesn't work. A Bosch USA made unit is $275 (plus $100 core) and Poland made Valeo is $375 (no core). I think I'll get the Bosch.

Note that the Bosch is a remanufactured (in the USA), not new like the Valeo. I have had great luck with Bosch rebuilds on my BMW. I got over 160k on my first, and currently have 100k on the second one, and still going strong. I have 371,000 miles on the car. It is a Bosch alternator, rebuilt by Bosch in the USA.

Note that Valeo is the original equipment manufacturer of alternators for your car, if that matters to you.
I'm curious where Bosch gets their cores from for the A6...or if they also use Valeo cores? (most likely, me thinks)

 

[willbur]

Note that the Bosch is a remanufactured (in the USA), not new like the Valeo. I have had great luck with Bosch rebuilds on my BMW. I got over 160k on my first, and currently have 100k on the second one, and still going strong. I have 371,000 miles on the car. It is a Bosch alternator, rebuilt by Bosch in the USA.

Note that Valeo is the original equipment manufacturer of alternators for your car, if that matters to you.
I'm curious where Bosch gets their cores from for the A6...or if they also use Valeo cores? (most likely, me thinks)

Those reman Bosch's WERE great- not anymore IMO

 

[f355spider]

Those reman Bosch's WERE great- not anymore IMO

Mine have been great, but the current Bosch rebuild I'm on is about 6 years old...
What was your experience?

 

[willbur]

Mine have been great, but the current Bosch rebuild I'm on is about 6 years old...
What was your experience?

Reman electrics are a common interest here on BITOG- Bosch quality has ben discussed numerous times and compared to other brands. Some ppl post Bosch was great but recently went chicom and its quality went down. It appears its now best to buy new, repair yours at a local rebuilder, or find a salvage yard low milage unit. I only buy new or from a dealer.

 

[f355spider]

Reman electrics are a common interest here on BITOG- Bosch quality has ben discussed numerous times and compared to other brands. Some ppl post Bosch was great but recently went chicom and its quality went down. It appears its now best to buy new, repair yours at a local rebuilder, or find a salvage yard low milage unit. I only buy new or from a dealer.

Unfortunately new is not an option for many cars more than a decade old. BMW only sells remanufactured Bosch (by Bosch) in some cases. Was not aware of the change. That is disappointing.