Alternator not charging the battery

REVERENJAGUAR13

MEMBER
2002 PONTIAC SUNFIRE
2.2L
4 CYL
2WD
AUTOMATIC
155,000 MILES

My alternator seems to not be charging my battery because I have to charge my battery with a charger and then it only runs for like 10 minutes before it drains. I've tested and there is 11.8 volts coming from the alternator. I haven't tested the wire at the battery yet because the wire goes up behind the engine and disappears so I can't follow it and I can't seem to find a diagram for it.

2 Replies

JACOBANDNICKOLAS

MECHANIC
108,320 POSTS

Hi,

It sounds like you are correct. With the engine running, the alternator should be producing around 14v.

If you want to, follow this link and let me know the results. The link explains how to test an alternator.

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Let me know if that is something you can perform. If you can, let me know the results.

Take care,

Joe

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Friday, April 29th, 2022 AT 8:23 PM

SQM

MECHANIC
6,383 POSTS

Hello,

It sounds like you have a bad alternator.
You should have 13.6V-15.2V from the alternator, as you are only getting 11.8V, it is likely bad.

You can also bench test the alternator to make sure that it is indeed faulty. Most auto parts stores have bench testers for alternators. You will simply have to remove the alternator and have them test it.

Here are a couple of helpful guides:

https://www.2carpros.com/articles/how-to-check-a-car-alternator
https://www.2carpros.com/articles/how-to-replace-an-alternator

I have attached diagrams for your reference.

Let me know of any questions.
Thank you.

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