The red battery light has come on at idle a couple times over the past couple days, but went away when I revved the engine. The battery is only 3 yrs old and reads 12.6v after sitting overnight. Alternator is original at just over 200k. At cold idle the voltage is reading 15v which seems too high to me. Once warmed up and no load settles back down to 14.4v. At idle and full electrical load (AC, fan, lights) voltage drops to 12.1v. At 3K rpm and full electrical load it's measuring 13.5v but drops significantly down into 12v range when the AC fans cycle on.

Seems like a faulty alternator but wondered if there was anything else I should check before ordering one.

 

The ELD device failure would rather cause higher than normal voltage and will set a code without turning on check engine light.
Check the condition of alternator fuse connections on positive battery terminal (corrosion can significantly lower available alternator output there). If fuse connections are clean the alternator is most likely having issue. .

 

Don't have any stored codes, and battery terminals and all fuses are clean. The alternator connections are rusty though so will try cleaning those off and testing again to make sure the alternator is going bad.

 

Alternator was the issue. New one reads 14.4 volts at idle no accessories on. As accessories are turned on up to full electrical load it never drops below 14.1 volts.

 

Glad to hear you found the solution to your problem. Do you know what exactly was wrong with the alternator? Did the corroded terminal have any affect on it?

 

Thanks for posting back with the solution!

 

I wish I had time to take it apart to figure it out and fix it myself as the bearings still spun as smoothly as the replacement. But I needed a replacement quick as I don't have another vehicle for mine to be down for an unknown length of time. Cleaning the ground connection on the alternator had no effect. It was corroded around the connection but the metal-to-metal connection underneath the bolt was clean.

 

^^^ Thank you for taking the time to respond to my question.