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Discussion Starter #1
Today my Battery light came on and will have to pull codes tomorrow. I was checking online and came across this "battery temp sensor" that's under the battery and thought that this possibly might be it since its been reaching in the upper 90's. Does the 2008 Commander have one of these sensors under the battery? Can outside temps impact this or the Battery light on the dash going off.
 

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How old is your battery?..........Do you live in the hot climates?..... My initial indication of a bad battery, is my radio being on AM station in the am when I normally listen to satellite radio. This usually happens for 2-3 days before my battery dies.
 

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Discussion Starter #3 (Edited)
Well I got my scan tool hooked it up and started the Jeep. The Battery dash light came on but no error. I looked at the live data on my scan tool but all looked normal. I saw this but not sure what it meant ..."load_pct(%) 33.3" Anyway, I was sitting in the Commander with the a/c blowing cold and suddenly the a/c turned off and the heat came on. Then the jeep died. Still had some dash lights power but the jeep would not start. I checked the scan tool and noticed code P0562 System Low Voltage. I put my hand on the battery and it was quite hot to the touch. Now I'm stuck with my Jeep dead in the driveway. Does this sound like an alternator job? Is it a tough job to swap out the alternator on the Hemi?

 

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Go to a place that will check you complete charging system. a couple of years back it cost $12. An auto parts store may do it for free.
 

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The Battery Temp Sensor is used by the PCM to set the charging voltage of the electric system. The cooler the battery, the higher the voltage and vice-a-versa. It has no associated warnings that I am aware of. As well, the ambient temp sensor on the Commander may be used to perform that function with an algorithm to translate what the battery temp should be from the conditions.


The Battery Light on the Dash, should be explained in the Owner's Manual, but it usually means an electric system fault detected, usually one of 3:
  • Electric System Voltage too Low, 9 volts or less
  • Electric System Voltage too High, 15 volts or more
  • Fault detected in Field Control of the Alternator, the voltage doesn't respond to PCM making changes in the field control of the alternator
The most important thing to remember, if this light turns on, you're likely running on battery power, which will soon go dead and make the car go dead. Its possible the alternator and battery are going all screwy and messing up the electric system and something even worse could happen, but you'd see other signs.

Heat can kill a weak car battery, a bad battery can drag down the electric system voltage.

You need to put a multimeter on the batter with the vehicle off and running. If you have a battery charger, even better to troubleshoot.
 

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Unfortunately I'm dead in the driveway. When I get home from work tonight I'm going to put in a good battery I have in the garage and see how many volts the alternator is outputting. This might clear things up... I hope.
 

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Thanks for that Mongo. Sounds like you know your stuff. Hopefully the alternator output reading will help. Thanks!
 

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Remember, a good battery should have at least 12 volts. Check it before connecting the cables. Check it after installing the cables. Check the voltage with the ignition on but engine NOT running and engine running (preferably AC and all the other electric accessories off).

Engine running, the alternator should be making more voltage than the battery, usually at least 13 volts, especially more than the voltage with the ignition on but the engine NOT running. If its the same voltage with the engine running as it was with the ignition on but the engine NOT running, likely the alternator is dead and NOT producing any current/voltage.
 

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Discussion Starter #11
I finally hooked up my multi meter to the "known good" battery and it read 12.7V- Not running.
I started the jeep up and the initial reading was 12.19 then 12.12 then 12.07 then 11.90 then 11.81. I turned on the a/c and it stayed around 11.80. So I'm assuming that the alternator is not charging and is dead. I did hear a high pitch whine on startup but that soon went away.
Is it safe to say that I need to put in a new Alternator?
 

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Yes, that sounds like a bad alternator, as well, most auto stores have a tester that they can test the alternator, so take it off and have it tested before you buy a new or rebuilt alternator.
 

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Discussion Starter #13
Thanks will do that. One last question. I put a slow 2amp charge on the original battery that is about two years old (found the receipt) and the multimeter reads 12.7 volts on it. Is this a healthy battery or should I just replace it?
 

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The battery was drained dead and you're doing a trickle charge on it, it should be good. I've seen a fully charged battery up around 13V, but 12.7V is more than respectable. If you're doing a 2amp charge, you should do it for 24 hours if you can.
 

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Discussion Starter #15
Removed the alternator this morning. Wasn't too bad- had to remove the air filter housing in order to get that alternator slid out. I brought it over to my Chrysler service dept. and asked if they can check this out. The told me it was dead as a doorknob. I did notice that some of the internal copper wire was burnt and falling out of the alt. opening. I ordered a new Denzo Alt. @ 370$- yes new not re-manufactured. I just didn't feel like dealing with a reman. one. Expensive I know. I also ordered a new serp. belt. Will hopefully get this done tomorrow. Appreciate your help!
 

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Discussion Starter #16
So I saw a video on you tube about alternator diode testing on an alternator on the bench. I decided to give it a try with my old alt. I put the multimeter on the diode testing spot and attached the positive multimeter wire to the B+ terminal of the alt. and the negative to the metal housing. The MM read "1"so I switched wires negative to the B+ terminal and the positive to the metal alt housing and the MM read 675. Now what this means I'm not sure. I was hoping someone could educate me about these readings and what it means. I feel like learning something today while I wait for the Alt. to arrive.
Thanks!
 
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