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Battery Light Comes on Periodically for 2004 Expedition XLT 4.6L

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I have a 2004 Expedition XLT with a 4.6L engine.  I wonder if someone has run across this or if anyone is very familiar with the Expedition's electrical system, I can get some advice.


I can pretty well describe the issue sequentially:

I have a volt meter plugged into the 12V cigarette receptacle.  It displays the system voltage, which is usually 14.3 or 14.4 volts.  This device helps characterize what is going on as you'll see.  By the way, I have a new  battery and I had replaced the battery thinking the issue was due to an old battery.  This is not the case.

1. I start up the car and no battery light shows, which is fine.  I see my volt meter showing 14.4 volts.

2. After a bit, maybe 10-15 or more minutes, the battery light will turn on.   At precisely this time, the voltage showing on the volt meter goes down to 12.7 or so.

3. The volt meter will be seen to display 12.7 volts and bit by bit, over about 5-10 minutes, the voltage will go down, eventually to 12.0 or even. 11.9 volts.  NOTE:  The headlights become somewhat dimmer during this time.

4. Once the volt meter displays 12.0 or 11.9 volts, suddenly, the battery light turns off and the volt meter displays 14.4 volts.  The headlights become brighter.  It stays this way for about 5-10 minutes and then repeats the sequence over and over, starting again at step 2.


It's obvious that the system is running off the  battery for a period of time and when the "juice" gets too low, the system starts charging again.  Does anyone know what component this could be that is failing?  For some reason, the system stops charging, but immediately starts charging when the  battery no longer delivers enough power.




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Check the pins in the voltage regulator for spread apart or corrosion. Also. Follow the battery cable from the alternator to the battery. Check the tightness and condition of the cable and ends. Also check the black connector on battery cable going to alternator. That’s what the tsb describes. That alternator is pcm controlled. Check those wires from the voltage regulator to the pcm for chafing also. 

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