Bad alternator or battery???

[E53blue4.8is]

Hey guys, I have a 2006 4.8is that I've had for a couple of months. Its had an intermittent issue that when driving all of a sudden, the dsc off, 4x4, and brake lights come on all at once. The radio screen would also go blank and I'd lose radio sound too. After all that, it would kick into trans failsafe mode. It's been starting to do it pretty every time I drive now. And if I shut it off while the lights are on, the battery is dead and I'll have to jump it. I'm not sure if it's the alternator that isn't charging, or there's a bad cell in the battery or something. Both were new in November and only have about 5000 miles on them. The previous owner had them installed at a midas location. Thoughts??

[EODguy]

What does your hidden menu say that voltage is while running?

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[E53blue4.8is]

It doesn't stay on long enough to tell. It always kicks off to tell me myself leveling air suspension is inactive.

[crystalworks]

Alternator. And if the battery has been flat multiple times without being trickle charged back up... it might be dead again too. Midas probably used a rebuilt or aftermarket alternator that isn't performing.

[E53blue4.8is]

That's what I was figuring too. Just wanted other people's input before i dropped the money on it since they aren't cheap.

[crystalworks]

Originally Posted by E53blue4.8is

That's what I was figuring too. Just wanted other people's input before i dropped the money on it since they aren't cheap.

Monitoring your voltage is the best way to definitively diagnose it. But that's my guess and where I'd put my money.

[SlickGT1]

I don’t know. Mine was voltage regulator. Like $40 from bmw. Car was doing some
Stupid shit too. Trans failsafe, susp inactive, brakes light would turn on. Navi reboot. Guess what. Overvoltage. Not Under voltage.

I would scan it. Inpa will pick up a code if it’s low bat or over voltage.

[E53blue4.8is]

Originally Posted by SlickGT1

I don’t know. Mine was voltage regulator. Like $40 from bmw. Car was doing some
Stupid shit too. Trans failsafe, susp inactive, brakes light would turn on. Navi reboot. Guess what. Overvoltage. Not Under voltage.

I would scan it. Inpa will pick up a code if it’s low bat or over voltage.

You don't happen to have a part number, do you?

[crystalworks]

Originally Posted by SlickGT1

I don’t know. Mine was voltage regulator. Like $40 from bmw. Car was doing some
Stupid shit too. Trans failsafe, susp inactive, brakes light would turn on. Navi reboot. Guess what. Overvoltage. Not Under voltage.

I would scan it. Inpa will pick up a code if it’s low bat or over voltage.

It probably is the VR. When mine failed it would have both under and over voltage issues. I consider a VR failure an alternator failure and just replace the whole thing but, like yourself, many here have just replaced the VR and been back in business.

[andrewwynn]

i rebuilt my alternator with a $20 kit (for Valeyo). vs $325 for whole alternator.