Is it normal for the voltage to vary while driving at a constant speed or while sitting at idle? I had my scan tool hooked up and the voltage varied between 11.5V and 13.8V at idle, and while driving down the hwy at 65mph, the voltage would vary between 12.7V-13.6V. In both cases, the readings were erratic--it never stayed too long at one end or in the middle, it was just all over the place. Any ideas?

 

time for a new alternator bud, mine did the exact same thing LOL. I tried changing the brushes & even tightening the back contact up with no success, either a phase is on its way out or a short in the stator winding or something.

Hope this helps, Matt.

 

So, if i take it off and run it over to Advance or Auto Zone they should be able to test it and tell for certain, right?

 

It would be a diode going out probably. 11.x is low period. It shouldnt ever drop that low. It should always be over 13 or so. Id just let it go till it dies. May last a long time...

 

normal ratings are around 13.8 to 14.2..... Also get a load test for the battery, too... It will give you an idea if your cells are weakening....