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Hello! I have a 2010 Sonata that will no longer start without a jump. Battery tested 12.7 but needed a jump to 14 to start. No power at all when not jumped. In the few weeks prior to car quitting all of a sudden my husband noticed the interior car light was dimmer than normal but that is all. Worked great until it just wouldnt start. The mechanic said he found the body ground had a 9.8 volt positive charge as well. They removed the harness wire from fuse box that feeds alternator and positive charge went away. Alternator was replaced andcharge remained. Visually inspected wiring - no obvious issues. Need to take it 90 miles away to an electrical specialist - hoping someone might have insight before going on a wild goose chase and spending a fortune. Hope someone can help. Thanks!
 

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The mechanic said he found the body ground had a 9.8 volt positive charge as well.
If you had got an electrical specialist (AKA...AUTOSPARK) to check the car rather than a mechanic he would have known what that meant.
It means there is a high resistance between the battery negative terminal and the car body, usually caused by corrosion on the bolt that secures the main ground cable to the car body. Simply removing and cleaning the bolt and cable terminal, then scraping away the paint around the bolt hole should fix it.
 

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Positive Charge ???

Follow negative cable from battery to fender,, remove the lug from body.. grind paint to bare steel... slap some grease on bare steel, and put lug back in place..

Do same for cable at left frame rail adjacent to battery tray..

Now when done,, stick battery for voltage,, then move black test lead to engine on metal,, should reflect battery voltage within 0.2 volt of battery measured voltage



Remember kids --->> PAINT IS AN INSULATOR,,, NOT A CONDUCTOR....... SAME FOR RUST
 

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For complex electrical problems you can go to dealer. They can fully test all voltages from all wires and connections and address the problem instead of replacing unwanted parts from stupid mechanics, and only charge you $150. I think it maybe a loosen or corrosion connection. The new battery voltage should be 12.7V and jump to 14.xV when engine is running, so the battery is OK
 

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For complex electrical problems you can go to dealer. They can fully test all voltages from all wires and connections and address the problem instead of replacing unwanted parts from stupid mechanics, and only charge you $150.


Not a complex circuit problem....pretty basic.


I think it maybe a loosen or corrosion connection.



Yep...basic


The new battery voltage should be 12.7V and jump to 14.xV when engine is running, so the battery is OK
A voltage check is not conclusive. Need to load test, especially since it will start with a jump, although the real problem may be voltage is to low under normal starting conditions due to bad ground not allowing enough voltage to power the computer system.
 

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Yeah, what @AUTOSPARK said ...
High resistance in the terminals and grounding strap.
Can be fixed by cleaning with wire brush and elbow grease.
Corrosion is not always visible. This is why should always try to normalize the electrical connections first
Then go about troubleshooting if issue still exist after cleaning
 

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"For complex electrical problems you can go to dealer"

My son took his 2013 Kia Optima to the dealership once and it took them 4 days to figure out the battery neg cable was faulty....4 days!

Nope, I do my own troubleshooting.
 

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My son took his 2013 Kia Optima to the dealership once and it took them 4 days to figure out the battery neg cable was faulty....4 days!
Yeah there are a few similar horror stories on here about how the dealers diagnose electrical issues. The problem is very few dealers have an AUTOSPARK on staff so they are relying on mechanics to do a job that they aren't properly trained for. Putting your car into a dealer to have an electrical problem dealt with is kinda like calling out a plumber to fix the wiring in your house :surprise:
 

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Yeah, what @AUTOSPARK said ...
High resistance in the terminals and grounding strap.
Can be fixed by cleaning with wire brush and elbow grease.
Corrosion is not always visible. This is why should always try to normalize the electrical connections first
Then go about troubleshooting if issue still exist after cleaning
My grandson called the other day and complained about not being able to start his 2002 Corolla. I measured the terminals of the battery and got 13.5 volts. Moved the positive lead just off to the clamp and measured 3.2 volts! Dropping 10 volts. The connection did not look bad at all- no white or green crusties that
you would expect with that much of a drop. Connection was on the post very securely. Cleaned the terminals off, and all was well.
 

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You should have the main ground go back to the engine block. For some reason the Asian cars use the body for ground. This always causes issues as the cars age.

Get a pre-made ground wire long enough from an auto parts store long enough to go from the main body ground of the negative battery cable to the closest engine block bolt that can be used for a ground.

DC current needs to return to the source which is the alternator. When using the body for ground all the connections and joints develop resistance over time.
 
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