My wife was driving home from visiting her family 3 hours away and the battery light came on shortly after she got on the road. About 2 hours into the drive the light went out. Then came on again, then went on and off several times, and is now staying off. I checked the battery voltage when she got home and it was around 13 volts with the car off. With the engine running the voltage was up around 13.6 volts while the engine was hot. According to the FSM this is within spec on a hot engine. I tested again after it had cooled off a bit and it was up to 13.8 volts while running and under load (lights, a/c, radio on). Battery terminals are clean, 7.5A Alt fuse looks good, and I don't see any broken/bare wires running to the alternator.

I'm thinking that maybe the voltage regulator is starting to give up the ghost and am considering replacing it as we're travelling to see family later this week. It's not cheap though and is actually more expensive than a full reman alternator from any of the parts stores. Is there a way to test just the voltage regulator or is it just a parts darts situation? Any thoughts?

Brushes on the alternator need to be replaced.

Yes, it could be worn down brushes. That is usually the failure with alternators, but the intermittent component has me thinking it could be something else, like a loose connection, IC Regulator or Diode Kit.

I think I'm gonna call the dealership in the morning and see if they have the brushes and a voltage regulator in stock. If not, I'll get them on order and pick up a Napa alternator and keep it in the truck in case it gives up the ghost and I need to do a roadside alternator swap.

I'm also wondering if it could be a belt tension issue. Going to check that in the morning.

If it’s the OEM Alt my vote is for the brushes.

If you’re removing it to check connections may as well do brushes. It’s easy.


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Mine started to be intermittent as well. And you could revive it with a gentle tap on the alternator housing.

I got this kit: Alternator Rebuild Kit 2000-02 Tundra 3.4L w 80 Amp, 2000-04 Tacoma v6 – alternatorbrush.com

It really was only the brushes, but I messed up the diode pack removing the brushes (rust belt car that gets driven in the winter, rust never sleeps, SIGHHHHH) and ended up needing that as well.

Not sure why they put two loose brushes in the kit? I used the brush holder with the brushes installed. The bearings felt 100% perfect when I spun it, so I certainly didn't try replacing them.

Works perfectly again, hopefully I get another 250K out of it.

That's about as much attention a 'rebuilt' alternator gets, other than not dousing it in paint.

Well since I'm short on time and need to drive this thing 200 miles on Wednesday, I can't wait to order parts so I went ahead and ordered a remanufactured Denso unit from Napa. Supposed to pick it up at the store sometime today. I'm going back and forth between just installing it an being done with it, and just keeping it in the truck in case the current one fails until I can get the parts to rebuild the OE alternator.

Always easier to change it when planned vs unplanned.

if its truly a denso remanufacture, then I would just go ahead and swap out. Road side work is no fun,,,and you said your wife visits family hours away

Threw in the Denso rebuild and it's been fine ever since. Contemplating holding onto the OE one instead of getting the core charge back and rebuilding it as a backup.