On my Corolla I typically measure 12.6 volts before starting the car, then 14.5 volts right after starting it, then after idling in the driveway 10 minutes, 13.5 volts. However this depends somewhat on the temperature and how fully charged the battery was initially. Many newer cars use a more sophisticated alternator management algorithm and I think on those cars the charging voltage can be over 14.5 volts in some conditions.
At any rate, to drill down to the definitive answer to the question, replace the alternator. If it was bad, all will be good. If the alternator was good, you have simply purchased an alternator a little ahead of schedule. Not the end of the world.
It appears that could be my case as well no charging warning light comes on at all. In the service manual it says there is one so I guess that could be the problem. How would I go about checking the bulb?
The battery warning light will come on when you first get into the car and turn the key to ârunâ before starting. Read your ownerâs manual.
If it doesnât light up as described above with the key in âonâ & before starting the engine, youâll have to find the procedure to replace the bulb. It varies car to car, and that info is found in the factory service manual or AllData typically. Often the dealership will print it out for your if you ask and they arenât busy at the time. It might be more cost effective to go to a shop or auto electric place for something like this.
Thank you! I can print out the section I need myself. Hopefully I can do it myself if not then yea I will take it to a shop.
Ok so I swapped the bulb from srs light because it is the same as the battery light. When I put everything back together the battery light still didnât come on but the srs one did so the bulb is fine. I guess the alternator is definitely the issue then.
Have you not had the charging system checked and if the answer is no, why?
I figured I should be able to do most of the checking myself. I checked all the ground connections for the battery and alternator they were all fine. I checked the voltage of the car under load and not underload. Not underload measured 12.6 and started to drop over time and underload lights dimmed and the voltage dropped even further. I checked the warning light bulb and it is ok. The battery is only a year old and is in good shape. The battery terminals are clean. Also the alternator is at least 2 years old.
I am trying to spend the least amount of money possible. Since the car is not registered I canât take it anywhere to have it checked without a tow. I guess I could just take out the alternator and have that checked but Iâll just replace it because I donât see what else it could possibly be. No check engine codes but there are problems with emissions according to obd2.
These are Hondas, but problem was usually a bad connection at the alternator:
It does sound like the alternator is the culprit. To prove this theory, many auto parts stores , both national chain and local independents, have a test fixture on site to test alternators. My local parts store provides that test gratis to its customers. You just have to unbolt the alternator and take it there is all. Takes about 5 minutes for the test.
Edit: ⊠from what I can see the way that light works, itâs powered on one side of the bulb from battery +, through the ignition switch , then to the light. the other side of the light goes to the alternatorâs voltage regulator plug, pin L. itâs a 4 terminal plug, the other 3 pins are labeled g, s, and fr on the diagram. Not sure if that is the color of the wire, or the name of the function the pin does. that bulb has a diode in it btw, so it has to be inserted w/the correct orientation or it wonât work. and the srs bulb might not be compatible with the alternator bulb btw, b/c of that diode. And it wonât light unless it is making contact with the voltage regulator, so a bad connection at the connector as mentioned above could cause this. if I were doing this the first thing Iâd do is remove that bulb and power it up on the bench (or just use the carâs battery) and make sure it lights in one direction, but not the other. if it does light in one direction but not the other, after that Iâd probe the connections where the bulb plugs in, one should measure 12 volts, and the other should measure near ground during a condition when the bulb should light, for instance when the key is in âonâ but the engine isnât started.
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That was actually suggested a month ago.
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Yep it was and its extremely inconvenient for me to take out the alternator then have to pay someone to drive me 30 mins away to test it and 30 mins back so Iâll ust take the chance of putting a new alternator in because thats most likely the problem.
Thank you very nuch for all your help 
WTH . . . over a month ago, Volvo suggested unbolting the alternator, and taking it to Autozone, for a free test
Yet George now gets credited with the solution . . . ?
I tell you, this green check mark âsolutionâ box to click was a LOUSY idea
But weâve already discussed this
@cdaquila . . . please talk with your bosses and urge them to get rid of the feature. Itâs not working
And I donât even have any skin in the game, so to speak, because taking the alternator to autozone for testing wasnât my idea
I gave George it because he provide much more info and solutions then volvo
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You credited the wrong man, IMO
Volvoâs advice was essentially the same, and he gave it to you in early November
If youâd taken his advice back then, the car might have been fixed a long time ago
I donât mean to sound harsh, but Iâm calling it as I see it
A little clarification is in order perhaps. From what I can tell the OP has never taken the alternator to AZ or anywhere else for testing.
Cool I wonât be able to drive it for a few more months anyways so doesnât bother me. Plus I wanted to make sure I tested everything I could on my own first before I brought it there because its extremely inconvenient for me. I figure if I have to take the alternator out Iâll just replace it and if its not the problem go from there. Since Iâll be ordering the part online.