Battery dash light. Reading 12v while running. New battery. Bad alternator?

Took a trip from MA to NJ, and the battery dash light kicked on just crossing the GWB with voltage dropping to 12v on the dash meter.

Grabbed a battery to replace hoping it's just that, but I'm worried it's the alternator. Well, the voltage on the dash only reads 12v with the new one in. Since it was 10pm when this happened I was only able to get the battery from Walmart, and being 250 miles from home I'm really hoping it's just a dying alternator and not a dead one. Would like to make it home for the 10+ hour shop repair.

Thoughts?

Going to take it to AutoZone in the am to test the alternator regardless and pray. Truck is at 181k miles.

(Not sure if related, but the TPMS light flickered on then stayed solid around Bridgeport, CT, then went away after 5 minutes. Voltage was around 14v on the battery dash meter then, so I'm assuming the alternator was charging fine at the time?)

 

TPMS has nothing to do with the battery or alternator. Elevation and temperature changes will affect tire pressure, so that could be it or, assuming you've not changed them and it's 10 years old, it could be that you have a TPMS sensor that is starting to die. Either way, it's likely not related to your alternator/battery issue.

181K miles for an alternator is pretty good, actually. Have you replaced it before this?

 

Alternator was never replaced.

 

Ah, it's an easy possibility that it's shot then.

I'd also check the battery cables and grounds to be sure everything is properly tightened. Check the belt for looseness and all the pulley's/tensioners. If the belt is loose it may not be gripping the alternator pully enough to properly run it. Had that kind of an issue in an old dodge truck. Wound up being the AC compressor's clutch that was making the belt skip a bit.

 

Yeah, that's what I'm afraid of. Serp belt was changed at 160k. Now that it's light out, going to check the cables and such and head to AutoZone for the test. My gut has been telling me I should look into replacing the alternator as a precaution for a couple months now, but no signs of issue were apparent until this trip.

I'll report back later after this look.

 

Well, the connections appear solid. Local AutoZone said the charging system failed, but they forgot the paper in the tester so no printed results. Either way, on the drive to the AutoZone my OBD II registers 13.1v to 13.6v on the system. AutoZone said I should be able to make it back to MA, but I'm going to stop by the Costco and pick up a spare 27F battery to keep in the bed. Thankfully, it's going to be 50s and sunny all weekend.

Looks like I got another 1k repair job ahead of me. I may as well replace my terminals and battery tie down while I'm at it. Any good recommendations?

 

https://www.maniacelectricmotors.com/alternator-rebuild-kits-2010-2014-toyota-tundra.html

$40 and a few hours of your time.

 

12v while running isn’t normal. Cold start should see 13.9-14.0. Warm idle should be at least 13.2. 12v is literally just battery voltage.

 

Made it back to MA, but my alternator is definitely shot. It ded.

On a similar note, we can estimate 80 to 100 miles of travel on a fully charged battery in a 2014 Tundra, depending on what accessories you're powering and how fast you drive. I squeezed about 100 miles by dimming all the dash lights, shutting off the head unit, disconnecting my amps, and driving 65mph most of the way.

 

Glad you made it safe. Now for an alternator swap and recharging the battery.