Automotive ?? 2004 Impala battery 0.09V when cables connected, 12.7 when not, why?

   #1  

MossRoad

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A friend has a 2004 Impala. Turned out his starter was bad. That is taken care of. However, while he was troubleshooting it, he noticed that if he put a volt meter across the battery terminals, it only read about 0.09V. If he disconnects the battery cables from the battery, and puts the meter back on, it reads 12.7V.

We put the meter across the terminals of other vehicles, and it reads 12.7V with the battery cables connected.

Why does his read 0V when the battery cables are connected? Is it something to do with the anti-theft system? What would cause that? Just curious, as I’ve never seen that before.
Thanks, in advance.
 
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Mendonsy

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The only way that I have seen something like that happen was with a battery that had a bad internal connection between cells.
 
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Ford850

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Is he taking his reading from the cables or directly from the battery posts when checking while cables are connected?
 
  
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MossRoad

MossRoad

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We took them from the side of the post bolts where you’d connect jumper cables (its side mount terminals), we took them from the top of the bolt heads, we took them from the battery cables... its a head scratcher.
 
  
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MossRoad

MossRoad

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The only way that I have seen something like that happen was with a battery that had a bad internal connection between cells.

Me too, however, the car starts and runs fine. And it measures 12.7V at the battery with the cables disconnected. I was thinking perhaps the battery terminals themselves are intermittent connection inside the battery and tightening the cables had something to do with it, however, it runs and charges fine. I’m stumped.
 
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RNeumann

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What does the meter show when the vehicle is running? The side post design practically limits your ability to read anything besides the bolt when the cable is attached. The bolt has a layer of corrosion on it that isn't allowing for a good reading. The bolts and battery cable ends need a little wire brush work.
 
  
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MossRoad

MossRoad

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We went out and scraped an area on the bolt and there was a pretty good layer of corrosion. Meter reads fine now, 12.7V. Slaps forehead! :banghead::duh::duh::duh:
 
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/pine

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We went out and scraped an area on the bolt and there was a pretty good layer of corrosion. Meter reads fine now, 12.7V. Slaps forehead! :banghead::duh::duh::duh:

Darn...That was a good mystery while it lasted...
 
 
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