Battery Drain thru Alt?
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Senior User
Joined: Nov 2006
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From: Northern New Mexico
Battery Drain thru Alt?
My 1 1/2 week old 2006 5.4L greets me every other morning with a dead battery. I am trying to determine if the problem is with the alternator allowing current to flow back through when the vehicle is parked.
I ran the engine at idle and disconnected the negative terminal on the battery.
Engine continued to idle.
Turned on the headlights and the engine died immediately.
Am I right that this test indicates either a weak battery or an alternator with a bad diode allowing current to flow back?
The battery had been kept on a charger for over ten hours at the trickle rate, so it shoulld have been fully charged.
Tonight, I was thinking of disconnecting the negative battery terminal for overnight. If the battery still has current in the morning then the problem is likely the alternator, right?
Any advice is appreciated. I was supposed to leave on a road trip tomorrow and would like to have some confidence in the vehicle.
I ran the engine at idle and disconnected the negative terminal on the battery.
Engine continued to idle.
Turned on the headlights and the engine died immediately.
Am I right that this test indicates either a weak battery or an alternator with a bad diode allowing current to flow back?
The battery had been kept on a charger for over ten hours at the trickle rate, so it shoulld have been fully charged.
Tonight, I was thinking of disconnecting the negative battery terminal for overnight. If the battery still has current in the morning then the problem is likely the alternator, right?
Any advice is appreciated. I was supposed to leave on a road trip tomorrow and would like to have some confidence in the vehicle.
Elder User
Joined: Mar 2005
Posts: 878
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From: Cornelius, Oregon
Originally Posted by Flame Out
I ran the engine at idle and disconnected the negative terminal on the battery.
Engine continued to idle.
Turned on the headlights and the engine died immediately.
Am I right that this test indicates either a weak battery or an alternator with a bad diode allowing current to flow back?
Engine continued to idle.
Turned on the headlights and the engine died immediately.
Am I right that this test indicates either a weak battery or an alternator with a bad diode allowing current to flow back?
Originally Posted by Flame Out
Tonight, I was thinking of disconnecting the negative battery terminal for overnight. If the battery still has current in the morning then the problem is likely the alternator, right?
I would also take the vehicle to a local auto-zone or equivalent and have them test the battery and alternator.
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Senior User
Joined: Nov 2006
Posts: 294
Likes: 3
From: Northern New Mexico
The fact that it died when you turned on the lights though tells me your alternator is probably not working correctly.
What you want to do, is put an ammeter on the battery (well techincally between the battery terminal and the batter cable) and look at how many amps are being drawn with nothing turned on. Then start pulling fuses one at a time to narrow down which circuit the draw is in.
Thanks for the advice. I wrote it all down for future reference.
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