Alternator Problems?

I am an older woman and have not the slightest clue as to car repairs, that was something my late husband did for me. The mechanic we have used for years is telling me that my car has alternator problems. Can you please tell me what this would include?

Dornell C.

Hello there Dornell,

Thanks for your email.  Did you take the vehicle to the mechanic for a specific reason?  Usually when I see problems with alternators it is a battery issue, like the battery does not stay fully charged or drains down while you are driving and you have to jump start or charge the battery to start the engine.

I am going to assume one of those issues is taking place. Most cars have a battery warning light, or a “charge” light on the dashboard.

If you see a red warning light, usually of a battery symbol that can be caused by an alternator that is not charging the battery, a bad battery, or a loose connection at the battery keeping the alternator voltage from recharging the battery.

If the battery is new, or you are using a known good battery and you constantly have to charge or jump start the battery and the red light is on the dash, that would be a good indicator of an alternator problem.

Now, I have seen (many times) a red dash light that is ON but there are no problems with the battery going dead. This is usually an internal problem with the alternator called a “diode trio” that will set the warning light ON but still allows the alternator to produce the charge to the battery. I see this more with GM vehicle than any other.

If this is happening, you will need to have this alternator overhauled or buy a new or rebuilt alternator from the mechanic. It is probably a matter of time before the rest of the internal parts of the alternator begin to fail and leave you stranded with a dead battery.

A bad alternator can also cause an electrical “drain” and suck the power out of the battery, even with the engine OFF.  The diode inside the alternator can act as a ground when bad and will basically suck out the battery power like if you left your headlights or interior dome light on.

If you have a “drain” that is sucking down the battery as the car sits overnight you can simply unplug the electrical connector at the alternator to determine if the alternator is the culprit of the drain.

How to test for a parasitic battery drain video, very helpful.

In any case, any alternator or battery charging situation should have this test performed:

1. Load test the battery, can the battery HOLD a charge or is it dead inside?

2. Check the alternator output, can and does the alternator send voltage to the battery?

3. Check the system for a voltage drain, what if anything is draining the power from the battery?

4. Check belts and battery connections, is the belt on the alternator, are the battery cables clean and tight?

You need to have your mechanic check those items to be sure of what is at fault.

I hope that helps,

Please share this with your friends,

Austin Davis