Check Charging System (Zombie Battery)

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NaviGatorHunter

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I know there are similar posts already, but I haven’t seen one with this exact recipe…

I purchased a 2004 Lincoln Navigator with 239,000 miles on the odometer. Over the two-hour drive home the “Check charging system” flashed periodically and the battery light came on periodically (though not always at the same time).

I made it to within three miles of my home and every light in the truck went out (dash lights, radio illumination, gauges, inside was completely dark) and the headlights were very dim. The engine continued to run as normal but all things electric were weak or in-op.

I limped into the driveway and shut her down. I tried to restart and it sounded like a dead battery (click, click, click) but no start. So I assumed that the alternator finally gave up and I had limped in on the remaining battery voltage.

The next morning, for giggles, I decided to give her a try and it started as if nothing had ever happened. I’m getting 13.5v at the battery with nothing turned on and 14.2 with fans and lights and radio on.

I’ve read about the fused link between the battery and alternator but I’m puzzled as to how it would cause this array of symptoms. If the fused link has failed then there should be no charging. Right? And it wouldn't explain the battery coming back from the dead... would it?

Could this be a computer issue? Any tests that a layperson could do to diagnose a computer failure (Failing)?
 

Yupster Dog

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DJ04

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I have the same symptoms, MOL. I suspect the alternator's internal voltage regulator does not communicate properly with the PCM when it (the voltage regulator) gets hot. When I start the truck in the morning after a night of inactivity it works fine. Good voltage to the battery etc. etc. I can drive around for 5 or 10 miles, come home and park, turn the key off etc. and then as soon as I can, when I start the truck again (it starts right up) the Check Charging System and battery light may well be on and the voltage at the battery is less than base voltage. If were to I drive around in this way sooner or later I would run out of battery voltage. I have run out of battery voltage before during regular use of the truck. When you run out fa battery you stop.
The Factory Manual has a test, voltage drop under load (that means hi beams, A/C full blast, rear window defrost on), if less than .5 V (500 mV) means "Replace Generator". That seems counterintuitive except that if the generator is not putting out any voltage to speak of, there won't be any voltage drop between output terminal and positive battery terminal. When I do that test with the Check Charging System and Battery light on I get something in the neighborhood of 2.4 mV, way less than the 500 mV the Factory test calls for.
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