Ok I have a 1999 Ford expedition with the 5.4 liter engine. I replaced the Battery and alternator about 3 months ago because battery was dying. Well everything was good until last week when my battery light came on. I checked the voltage with a multimeter and was getting about 13.2 volts with engine running at idle and when I turned on fog and head lights the alternator was putting out about 12.2 volts so naturally I replaced the alternator again. So I got the new alternator and it is about 13.3- 13.5 volts at idle I held a rev at about 2500 rpm and this value may have changed to maybe 13.6 volts. This seems very low to me. I also tested the battery without the engine running it was at 12.0 volts. Do the values seem low to anyone else? With the new alternator it is not going down in voltage when I turn the headlights and fog lights on and I have no battery light yet. Its getting close to winter and I don't want to be stranded. Please let ne know ya'lls thoughts.


Thanks Chris

 

13.8-14.2 is optimal charging voltage. Check the 20-amp fuse #11 in the under hood fuse box to make sure it's good.

 

I was using a scan tool and it was telling me the wrong info. I used a regular multimeter and it checked out great. Thanks For replying.

 

Lesson to be learned...the OBD connection voltage can be 1/2-3/4 volt lower then using a measurement at the battery. It can also be 1/2 volt lower there then at the alternator terminal if the connection isn't good. Corrosion, too small a charging line, etc can give you false readings.
When possible, measure directly off of the alternator terminal.

 

How do you know the multimeter is giving the correct reading? Just because it's reading what you want the voltage to be doesn't mean it's accurate. At this point you need a third reading from another meter to confirm.