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Old 07-06-2019, 10:08 AM
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Battery Light On

hello gents,
thousands apologies if this questions has been answered before

my battery light comes on on my JKU 2007, when i don't accelerate properly. what i saw that if the light stays on, the battery doesn't charge, and eventually the battery dies. BUT if i restart OR i switch on and off the ignition (even while driving ) all goes back to normal.

i read somewhere that this can be a "software" issue? that the ecu needs reflashing... but i couldn't find this post again...

your help, input, ideas, hints... are appreciated

thank you
and have a good week end

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Old 07-06-2019, 11:51 AM   #2
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Old 07-06-2019, 01:15 PM   #3
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I would start by having the battery checked and then the alternator to make sure it's putting out like its supposed to
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Old 07-06-2019, 01:18 PM   #4
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It could be a software issue or a lot of other things but if it came in our shop the first thing I would focus on is the alternator and battery. Sounds more like an alternator issue but there is so many computers in cars anymore it’s hard to say without testing stuff.
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Old 07-06-2019, 03:54 PM   #5
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^ This. Take it to any auto parts store and have the battery load tested and the output of the alternator checked. The latter can be done with a simple volt meter - it should read between 14.2 and 14.5 volts. Too high (16v for example) can be as bad as too low on the alternator output.

How old is the battery? If it is more than 2 years, it may be the battery. Unless you have a very high end battery it is unlikely to last much more than 3 years. There are exceptions of course. If you have a battery charger, I would use that and have the battery tested when it has a full charge. Some of us have a battery tender that you can leave hooked up and it keeps the battery at full voltage.

Even when the battery puts out 12 volts and is fully charged, if it is dying it will fail the load test. When mine in the TJ failed about 18 months ago, with a full charge, it would start the Jeep, but after sitting for two days, nothing. Charged up again, same thing.

The days of weak groaning cranking of the engine are over. The computer now will not even start to crank if the battery is not up to snuff. Then if the battery is up to the task, go to the alternator. If the alternator is putting out properly, then go to the next step.


Many on here will tell you to go with a high end AGM battery, but unless you plan to use it heavily and keep the Jeep for many more years, I wouldn't. When I replaced the battery in my TJ early last year, it was with a basic battery from a battery specialty house - their house brand and it and a new battery connector was about $110. And I intend to keep the TJ for many more years.
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Old 07-06-2019, 05:28 PM   #6
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Quote:
Originally Posted by rgreen65 View Post
^ This. Take it to any auto parts store and have the battery load tested and the output of the alternator checked. The latter can be done with a simple volt meter - it should read between 14.2 and 14.5 volts. Too high (16v for example) can be as bad as too low on the alternator output.

How old is the battery? If it is more than 2 years, it may be the battery. Unless you have a very high end battery it is unlikely to last much more than 3 years. There are exceptions of course. If you have a battery charger, I would use that and have the battery tested when it has a full charge. Some of us have a battery tender that you can leave hooked up and it keeps the battery at full voltage.

Even when the battery puts out 12 volts and is fully charged, if it is dying it will fail the load test. When mine in the TJ failed about 18 months ago, with a full charge, it would start the Jeep, but after sitting for two days, nothing. Charged up again, same thing.

The days of weak groaning cranking of the engine are over. The computer now will not even start to crank if the battery is not up to snuff. Then if the battery is up to the task, go to the alternator. If the alternator is putting out properly, then go to the next step.


Many on here will tell you to go with a high end AGM battery, but unless you plan to use it heavily and keep the Jeep for many more years, I wouldn't. When I replaced the battery in my TJ early last year, it was with a basic battery from a battery specialty house - their house brand and it and a new battery connector was about $110. And I intend to keep the TJ for many more years.
I agree optima battery’s are over kill for most people BUT I left my headlights on once all night long and came out and my car started right up the next morning. It made me a firm believer in them. And considering some places are charging 150 for a regular battery now and you can get a red top optima for around 200 if you shop around...plus they look really cool lol I guess I’ve got pretty far off topic here.
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Old 07-07-2019, 05:49 AM
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hello gents,
to Old Dodger: thank you for the welcome

to answer the battery question: it is less than a year old. but no it's not the cool looking one maybe looks matter?

i guess , since the second test is the alternator, i will do that once i hit the issue again... but why would the alternator (if it is the culprit) work again after the ignition start and stop (my work-around for the issue).

it reminds me of a sitcom (the IT crowd) , these I.T. guys when they receive a call the first thing they would tell the user "have you tried turning it off and on again?"

thank you hard rocker, autodoc21 and rgreen65 you rock !
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Old 07-07-2019, 08:10 AM   #8
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hello gents,
to Old Dodger: thank you for the welcome [IMG class=inlineimg]https://www.wranglerforum.com/../images/smilies/beer-drinking.gif[/IMG]

to answer the battery question: it is less than a year old. but no it's not the cool looking one [IMG class=inlineimg]https://www.wranglerforum.com/../images/smilies/biggrin.gif[/IMG] maybe looks matter? [IMG class=inlineimg]https://www.wranglerforum.com/../images/smilies/biggrin.gif[/IMG]

i guess , since the second test is the alternator, i will do that once i hit the issue again... but why would the alternator (if it is the culprit) work again after the ignition start and stop (my work-around for the issue).

it reminds me of a sitcom (the IT crowd) , these I.T. guys when they receive a call the first thing they would tell the user "have you tried turning it off and on again?"

thank you hard rocker, autodoc21 and rgreen65 you rock ! [IMG class=inlineimg]https://www.wranglerforum.com/../images/smilies/action-smiley-035.gif[/IMG]
Only thing I could say about turning turning stuff off and on is maybe it’s a way to do a soft reset on electronics. It reminds me of iphones. Everyone that has had an iPhone for awhile knows sometimes they will get “wonky” and usually doing what they call a soft reset (which is just basically a way of turning it off and on again) will fix your issues. In my simple mind I imagine your alternator could possibly stop working and you turning it off and on again kicks it back into action. Hopefully it was just having a bad day and it never gives you anymore trouble.

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