Battery Light

Discussion in 'KJ General Discussion' started by William Allan Wydeck, Sep 17, 2020.

  1. William Allan Wydeck

    William Allan Wydeck New Member

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    A little back story;
    My daughter has a '07 Liberty. Last spring-2019, she called me and said the Lego light was on(battery). I dropped my Jeep off with her and took her's home. The light did not come on. It did not come on fer a while. Then off and on.
    We leased her a new Civic because she is in college in Florida, we live in Michigan. So, since the Liberty will not be drove that much, I did nothing about it. This year it has been drove a little more.
    A month ago I had to drive it for about a week because I drowned my Jeep, killing the engine and had another put in.
    I was driving to work, and it would not shift, then shortly later, it would only idle. Then it died completely. Turn the key, nothing. Got it to work and we put the charger on it. Half way home, the battery light came on again.
    Now, I had the alternator rebuilt and put a new 800cca battery in it.
    The battery light is still on.
    What would cause the battery light to remain on now?
     
  2. Billwill

    Billwill Full Access Member

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    Best is to plug a Multimeter into the front Power Outlet point so that you can monitor the battery voltage.

    Either it is not charging properly...you should expect to see a voltage of about 13.4 Volts while driving...or something is shorting the battery out and draining the battery.

    The early KJs had a Temperature Sensor underneath the battery to sense its temperature...the PCM/ECM would slightly adjust the charge voltage. This sensor was no longer fitted after about 2004 I believe.

    My Export 2002 CRD had this sensor and a bad connection on the sensor...ground gone missing..caused this battery light to come on.

    So with the engine OFF voltage across the battery should be about 12.5 volts.

    While turning motor over it should not drop below about 10 volts.

    While engine is running it should show about 13.4 volts across the battery....if not then maybe the Alternator was not repaired correctly or you have an electrical problem somewhere.:(

    Check that the small connector on the Alternator is on firmly and check that the thicker cable on the Alternator is on firmly at the Alternator and firmly on at the Battery Positive terminal.

    Be very careful when working with this thicker cable from the alternator to the battery as it has a built in Fuse inside the cable so if you take a wrench to the connectors on this cable without first removing the Negative lead on the battery...your wrench touching chassis/engine will blow the fuse inside the cable.... "Fusable Link"... and you will have to buy a new cable. The cable color changes between year/model as they have different fuse ratings!;)
     
    Last edited: Sep 17, 2020
  3. William Allan Wydeck

    William Allan Wydeck New Member

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    Is the sensor under the battery box?
     
  4. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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  5. Billwill

    Billwill Full Access Member

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    I doubt the 2007 KJ has that sensor...stopped fitting it about the 2005 model...I do not have wiring diagrams for 2007 models!:(

    I should not have mentioned the Battery Sensor.....not relevant here!

    Monitor the voltage as stated and re-plug the connectors on the PCM and alternator.

    Some KJ models..maybe the 2007...have their Voltage regulators built into the Alternator itself and just get a wake-up call from the PCM...earlier models have the PCM doing the regulation. The 2006 Wiring Diagrams that I have show that pin1 on the small alternator plug goes to the PCM while pin 2 on the small plug....Black wire... goes to ground. This may be the same for the 2007 KJ!

    If your Alternator small connector plug has a Black wire on it...check that it goes to Ground or add a ground to it....Ground wires usually are Black or have Black as their main color with some other color stripe in it.;)

    May have to source another alternator if problem remains.:(
     
    Last edited: Sep 18, 2020
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  6. Billwill

    Billwill Full Access Member

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    Final note on the Battery Temperature Sensor.

    The 2006 KJ Manuals give a good description of this sensor, how it works and how to replace it with neat diagrams supplied.

    Turn over the pages to the Wiring Diagrams and this Sensor is nowhere to be seen because it does not exist!:confused:

    On the later KJ manuals Jeep did a lot of cut-and-paste so beware of errors!;)
     
  7. William Allan Wydeck

    William Allan Wydeck New Member

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    1. Just check, no sensor. I put a meter on the battery, all good. Started the engine, meter did not move. So I put an ohm meter on the red cable on the alternator and on the positive battery terminal. All good. So the alternator is not sending juice to the battery. Again, brand new 800cca battery and the alternator was just rebuilt. Starting to think it's the pcm/eco. Same thing happened on my 2018 JKU. Battery light was hit and miss. Dealer replaced alternator, it still happened. Then they replace the ecm. Problemed solved.
     
    Last edited: Sep 18, 2020
  8. Glock_19_9mm

    Glock_19_9mm New Member

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    Can you confirm you put the one lead of the meter on the alternator positive terminal and the other lead on the positive lead of the battery and read 13.4V?

    If this is the case you have an open circuit between the alternator and the battery (broken wire). You measure the source voltage across an open. If it was connected you would measure 0V (or a very low voltage) as you are reading the voltage drop in the cable. I would disconnect the battery and use the ohm scale of your meter and go from the positive battery connection on the cable to the alternator positive lead. That should read a short (or 0 ohms). If it reads open (or high resistance) you have to track that down.

    Unless the regulator is not in the alternator then there is something else going on.
     
    Last edited: Sep 18, 2020
  9. Billwill

    Billwill Full Access Member

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    I presume the OP had the engine switched OFF and with the Multi Meter set to OHMS he measured across the thick wire going from the Positive Battery Terminal to the large lug on the Alternator and got a reading showing that the lead was OK from end to end.:confused:

    If not so and to clear up any doubt...OP needs to put the meter on DC Volts and with engine OFF should measure +12.5 volts on the Red Battery Post with respect to ground and should measure +12.5 volts on the Large Lug on the Alternator with respect to ground.

    Start the Jeep up and repeat the above measurements and the voltages should both ramp up to about 13.4 volts if the Alternator is charging and the thick wire going from the Alternator to the Positive Battery Post..."Fusable Link" has not blown.

    With engine OFF measuring from Alternator Large Lug to ground we should get +12 volts with respect to ground if the Fusable Link is not blown.

    Final test for this Fusable Link is to power OFF the engine and remove the +Battery connector and measure the Link end to end for continuity.

    This Fusable Link has a built-in fuse that blows if there is a short on the Alternator end of the lead....to stop major current flow which could cause major damage or an engine bay fire!:(

    This Link gets blown often by fitting a wrench on the large Lug on the Alternator and touching the wrench to chassis....Battery should be disconnected before playing with the Fusable Link!;)

    If this Link is blown then that is the problem and a new Link must be fitted....color of the cable changes according to year and model because the fuse rating varies.;)
     
  10. William Allan Wydeck

    William Allan Wydeck New Member

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    It was the alternator. Changed that and all is good.
    Thanks.
     
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