Bad alternator?

Think I might have a bad alternator on my wife's 2015 Tahoe.

Had a slight whining noise show up about a week ago. I couldn't find anything right off the bat and it didn't affect the drivability so I was gonna wait until this weekend to troubleshoot further. Today she sends me a picture of a "Battery Saver Active" message on the DIC with the batter gauge at the low marker of the normal range. When she got home, I went out and did some preliminary tests with my multimeter. Just testing the battery with the car off, it's right at 12V. Cranking the car up and then testing (which I've never done before but ChrisFix recommends) the voltage was below 12, around 11.2. According to his video, that indicates a bad alternator. I can get an alternator from Amazon delivered on Sunday, or I can pay twice as much and get one from the local auto store tomorrow. Can I wait it out or is this something that will leave her on the side of the road? The message didn't show up when I had it running so I'm hoping it's just slowly on it's way out and not completely dead.



ChrisFix video:

It will likely leave her stranded, the battery alone will not provide the engine with the correct voltage long enough to get very far, I'd say park it until it's fixed unless you want more headaches

TXt3rr0r said:

It will likely leave her stranded, the battery alone will not provide the engine with the correct voltage long enough to get very far, I'd say park it until it's fixed unless you want more headaches

Click to expand...

That's what I'm afraid of. From where she took the picture today, she drove 35 minutes home with it like that today. Perfect timing for us, when everybody has somewhere to be at the same time.

If you have a battery charger and the battery is in good shape you could probably get by for a couple days with short trips. I probably wouldn't chance it.

bdbull said:

That's what I'm afraid of. From where she took the picture today, she drove 35 minutes home with it like that today. Perfect timing for us, when everybody has somewhere to be at the same time.

Click to expand...

That's how it always happens right???? If it wasn't for bad luck, we wouldn't have any at all!

Think I should replace the serpentine belt while I'm in there? Truck has 204k miles on it, and as far as I can tell it's never been done. I know I've never done it and we've owned it since 50k.

bdbull said:

Think I should replace the serpentine belt while I'm in there? Truck has 204k miles on it, and as far as I can tell it's never been done. I know I've never done it and we've owned it since 50k.

Click to expand...

Yes. Absolutely replace the belt and I would also replace the tensioner and idler pulleys.

Geotrash said:

Yes. Absolutely replace the belt and I would also replace the tensioner and idler pulleys.

Click to expand...

Any idea on part numbers? I think the tensioner is 12670574, but I can't seem to find a Tahoe specific part number for the idler pulley. Is it a generic part?

Edit: Is it one unit that contains both parts?

Did you try Rockauto and there is a discount code. Usually fairly easy to look up parts.

Tahoe14 said:

Did you try Rockauto and there is a discount code. Usually fairly easy to look up parts.

Click to expand...

Yeah that's what I usually use to lookup parts. There is no specific idler pulley for the Tahoe, and a search for idler pulley returns generic results. That's why I'm wondering if the part listed as the tensioner is actually both. I don't know enough about the parts to know. I just watch YouTube videos and do what they say.