Alternator voltage output acceptable range

My scangauge II is showing 12v to 12.9 volt output on my alternator. In the winter I’m a steady 13.8 to 14.1 volts. In warmer summer months in get 13.2 to 13.8v. What in acceptable
Alternator output or is it time to replace my 4 year old battery?

 

12.9 IMO is too low and you may have an issue

what is battery resting voltage after 30 minutes?
what is battery voltage with lights on, engine off?
can you leave your head lights on for an hour and still start it?

 

I have been idling for 45 minutes with A/C on holding a steady 12.8 / 12.9v.

 

that is a bit low, please do the other tests

 

I will, can’t do it now. Thank you.

 

IMO once it drops in to the 12's with everything on, it's time to think about replacing. Right now I'm seeing 13.2 - 13.4 with everything on during the day, on a cool summer morning with no draw I'll see 13.8 - 14.0 so that's fine for me. You might make it through this winter but keep an eye on it. In the meantime, I'd suggest to turn off all non essential components ~ 1 min before killing the truck to help charge the battery.

 

What does the service manual say about testing the alternator output?

 

I see 14.10V - 14.15V first thing in the morning immediately after starting with all accessories off. Once fully warmed up, I see 13.4V. My 2014 4Runner produces the same readings.

 

Something is sporadic, I just drove 250miles today A/C , headlights and wipers, held steady 13.5v. I’m going to replace the battery very soon.

 

If you were seeing 13.5V with all of that going on, I doubt you need a battery, but what do I know???

 

Mine's always been 13.0-13.2 with a fully charged battery, been driving awhile. Cold start, truck not driven in a few days and it will sit up at 13.5-14.0 for a bit, then go back down. Been that way for as long as I've had the Scanguage (5 years). The battery has been changed and made no difference. No problems. Normal from what I have seen. I worked at NAPA for awhile and used to test alternator and battery out in the parking lot on a variety of vehicles.

I would check your voltage at the battery posts and see what it is. You might have a voltage drop somewhere in the feed to the OBD2 port, which I wouldn't worry about if you have no other symptoms.

Idle with AC, etc running is definitely going to be worst case scenario.

 

My battery died yesterday. Got it replaced. Checked the alternator and I got a reading of 12.8

Cold start. Engine running, AC running, headlights OFF. I was getting 12.8v

I didn't do the other tests but that seems a bit low.
Thoughts?

 

I believe 13.2v - 14.8v is acceptable range @ 2000rpm

 

When we checked it was just idling in park. Should I redo the test

 

Your alternator does not supply much voltage/current at idle. You need to bring your idle up to ~950 to 1100 to see it kick in. Usually with your AC running it will tick up your idle speed some but it may not be enough to start the alternator charging. When you are testing, bring your idle up a few hundred RPMs to ~ 1100 to 1200 and see if you notice a change in the battery voltage/Alternator supply voltage. If with nothing on, you do not have over 13 Volts you need to be thinking about replacing the alternator or having someone else test it.

 

Check Post #3
https://www.tacomaworld.com/threads/bad-alternator.511627/

 

Local auto electric rebuilder(alternators/starters) that I've used for years told me to put the positive lead from the voltage-ohm meter on the alternators B+ terminal and the black lead to ground. More accurate alternator reading than red VOM lead to battery positive post - black VOM lead to battery negative post.