My girlfriend has a 2008 with around 120k miles on it. It's been pretty flawless but yesterday the RPMs started surging while idle and made kind of a high pitch humming noise when accelerating.

Today on her way to work she said the radio was going in and out, the battery light lit up and then the rest of the dash lights came on, and the speedometer stopped working.

Any idea what could be the problem? Could it just be the battery?

 

Alternator? If it still starts, it's not the battery...yet. A bad alternator can kill the battery though, and it will run dead and leave you stranded if the alternator isn't charging.

 

I was thinking it was the alternator too.

 

Do you have factory nav? If so, there is a diagnosis screen that can tell you your alternator/battery voltage while the truck is running.

 

Awesome, thanks for the tip. I'll check that out later tonight.

 

How to get to the diag screen:

 

I agree, but it is a start in the right direction. For example: if I see 12.0VDC on the screen while the truck is running, I would suspect the alternator more than the battery. I would then also know not to drive the truck very far to get it load tested, as it is probably just running off of the battery.

 

Yup. And with the truck off, the alternator is not charging. Load test = high beams and blower on high. This cost $0, needs 0 tools, and can be done in the driveway or parking lot.
http://www.aa1car.com/library/2003/us20310.htm

 

Well, she just called to tell me the vehicle wouldn't start when she was on her way back to work from her lunch break so it sounds like it's the battery that just died.

 

But you don't know yet if the battery was always the problem (not likely as it started previously), or the alternator (my bet).

 

get you a brush ring and replace that in the alternator. Less than $15

 

Thanks to those who offered their assistance.

It turned out to be the battery and the alternator. The battery was the original one that came with the vehicle so it's no surprise it died.

 

It was likely killed by the failing alternator, things like that don't fail in pairs on their own. Glad to hear you got it sorted.