Charging system fault - Page 2
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Thread: Charging system fault

  1. #16
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    Re: Charging system fault

    Try measuring the voltage between the ground and the BMS neg. That would be the black wire. I suspect a voltage drop at that location, possibly at the small circled connection to battery negative. From what I see, it appears that that wire should be connected to ground at the battery negative. D voltage drop there will confuse the BMS and lead to a code. Ray

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  3. #17
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    Re: Charging system fault

    Quote Originally Posted by RABarrett View Post
    Try measuring the voltage between the ground and the BMS neg. That would be the black wire. I suspect a voltage drop at that location, possibly at the small circled connection to battery negative. From what I see, it appears that that wire should be connected to ground at the battery negative. D voltage drop there will confuse the BMS and lead to a code. Ray
    You can't measure voltage where no potential exists... Negative to negative.
    But you can measure resistance... Which technically should be zero.

    Looking at the actual BMS, it's totally integrated within the battery post.
    There is no actual negative conductor for the BMS. It draws the ground straight off the battery post.
    I'll try to get a pic this weekend.

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  4. #18
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    Re: Charging system fault

    Actually, you can measure voltage, which is actually more accurate than resistance testing. The idea is to measure whether potential DOES exist. Since you mentioned that the BMS voltage was 11.4 volts while the battery voltage was 12 volts, and the positive side of the BMS showed 12 volts, it is possible for the ground side between the BMS negative and battery negative to have a potential, even though it should not. If, for example, the negative side of the BMS and the negative side of the battery had a potential of .6 volts, a resistance would exist where none should be there. The difference between the 12 volts on the positive side and the negative side, having a .6 volt potential would then be 11.4 volts, which you measured. That difference would lead to a code due to insufficient voltage "seen" by the BMS. Repairing the resistance between what should be ground and what is ground might clear your code. Ray

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  6. #19
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    Re: Charging system fault

    Using ohms law, which applies in EVERY situation, you can calculate resistance as low as .001 ohms. Suppose, for example, you have a no crank condition, and the resistance between the battery post and the battery cable end shows 0 ohms on your meter. Now, suppose you check the voltage between the battery post and the cable end while attempting to crank the engine, and you see 3 volts. If you assume that the starter, for example, draws 100 amps at initial crank, you have just determined that the three volt drop has measured a .003 ohm resistance. Does your meter have that resolution? You are now duplicating the conditions in which the problem has occurred. The resulting voltage drop at the battery has now provided the starter with 9 volts, making a cranking condition difficult at best. THAT is why I suggested checking the voltage between the BMS negative and the battery negative. You are correct in saying that you cannot measure a voltage potential where there is none. If, however, you check the voltage between these points, and you find the .6 volts, VOILA! It appears that you have a voltage drop somewhere, and, as was stated earlier, you may be overlooking the simple. The light on the dash is indicating something wrong, and using the same method the computer uses to find the problem will make troubleshooting easier. You mentioned that you checked the voltage at the BMS and the voltage at the battery positive. You can do the same thing at the negative side, and you are then covering ALL of the bases. Let is know... Ray

  7. #20
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    Re: Charging system fault

    Correction to thread by Ray: the resistance measured should read .03 ohms, not .003. Most DVM's show resistance readings to tenths of an ohm. ray

  8. #21
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    Re: Charging system fault

    Quote Originally Posted by RABarrett View Post
    Correction to thread by Ray: the resistance measured should read .03 ohms, not .003. Most DVM's show resistance readings to tenths of an ohm. ray
    Thanks for your feedback Ray... My bad. I was assuming you meant taking a direct voltage meter reading from a negative and a negative. I should of known you meant comparing two readings...
    And so today, I took a couple more measurements...
    First, before I explain what I did, here a pic of the BMS.
    As you can see, it draws its negative internally thru the actual battery post.
    The two pin Connector consists of the LIN that feeds to the body module and the battery positive feed... Which also comes off the battery post. In between is the fused link (0 ohm resistance).

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  9. #22
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    Re: Charging system fault

    Now the measurements... Checking the positive voltage feeding the BMS, I measured from negative to these points here...
    All points measured same voltage as direct battery post + and -




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    Last edited by RRToadHall; February 23rd, 2019 at 05:20 PM.
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  10. #23
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    Re: Charging system fault

    Next, I checked battery post + to the main chassis ground. No loss there either... Same as direct to battery measurement.

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  11. #24
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    Re: Charging system fault

    Now, at the BMS side (unplugged from LIN and +), I measured these two points to battery +
    The LIN voltage measured 9.5V (red arrow) and the yellow arrow (+ feed for BMS) measure 11.4V.
    For reference, battery voltage with engine off was 12.23V...

    I think to eliminate any issue at these points, I could use some help...
    Is any one able to meter these 2 points on there BMS?
    If the readings are the same, then I'd have to start looking elsewhere... Likely the LIN line to the body module.
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  12. #25
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    Re: Charging system fault

    Wungun: I am a little concerned regarding the battery voltage with the key off. A fully charged battery should measure 12.6 volts, or close. 12.3 volts indicates a partially charged battery. Have you checked the voltage between the battery terminal (negative) and the black wire on the BMS? That should show something under .2 volts. I suspect the LIN line is for the ECM to charge control, for the alternator. What is your battery voltage when the engine is running? One other thing to check is the voltage between the Mon wire on the BMS and the battery positive connection. You might also check the voltage between the alternator output (the red wire) and the battery positive, which should be about .3-.4 volts, depending on the current the battery is drawing. Your reading indicate a voltage drop somewhere. Your battery voltage while the key is off indicates a partially charged battery. You might also check the voltage on another battery to check your meter. Let us know... Ray

  13. #26
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    Re: Charging system fault

    https://www.rangerovers.net/forum/6-...eshooting.html


    Here are the generic basics follow through the tests with a basic multimeter. These are tried and true measurements to check your battery, alternator AND cables for resistance if you have cruddy cable ends at either end or a cable failing it will have high resistance and no amount of prayers are going to get perfectly good alternator to charge a battery.

  14. #27
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    Re: Charging system fault

    is there an echo in here? Ray

  15. #28
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    Re: Charging system fault

    There is NO black wire for the BMS. The wiring diagram just shows the BMS circuit. It draws negative power internally thru the battery post. This is all integrated. The only conductors that plug into it are LIN and +.
    Both my old and new BMS measured the same, so I'm eliminating it as the cause.

    When the fault first showed up, I metered the battery at work, and low and behold, 12.2V. I thought as you did, that the battery is going... So I replaced it with a 790CCA AGM battery.
    The new battery certainly cranks over the engine much quicker, but it still only measures around 12.2V between terminals.....
    I use a cheap digital meter... But the one I checked the old battery with was a good Fluke MM.
    I agree, that voltage seems low. But there is no other indication that its not normal. It's easily started the motor in minus 30 degree nights.

    With the engine idling, I'm seeing over 14V at the battery...

    Also, I'd eliminate the alternator as I've had this fault for maybe 6 weeks now....? Car still drives fine.

    Quote Originally Posted by RABarrett View Post
    Wungun: I am a little concerned regarding the battery voltage with the key off. A fully charged battery should measure 12.6 volts, or close. 12.3 volts indicates a partially charged battery. Have you checked the voltage between the battery terminal (negative) and the black wire on the BMS? Ray


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  16. #29
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    Re: Charging system fault

    @Ray.
    Yes,the LIN line is the communication line for the ECM/BCM.
    The MON line measures proper, full voltage going TO the BMS.
    From the BMS MON line to battery positive, its 11.5V as I mentioned.
    I need someone to check this on their Rover...
    And also LIN to +

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  17. #30
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    Re: Charging system fault

    Quote Originally Posted by RRToadHall View Post
    https://www.rangerovers.net/forum/6-...eshooting.html


    Here are the generic basics follow through the tests with a basic multimeter. These are tried and true measurements to check your battery, alternator AND cables for resistance if you have cruddy cable ends at either end or a cable failing it will have high resistance and no amount of prayers are going to get perfectly good alternator to charge a battery.
    Here is what I have... Couldn't get access to alternator for measurements...
    Car running voltage is less than when I last checked it (14.2V) this time.... Odd

    Engine off, all accessories on for 30 seconds, then off. What voltage ___12.17V
    2. Voltage across battery at idle (no electrical load) ____13.98V
    3. Voltage across battery at 2000rpm (no electrical load) _____13.98V
    4. Voltage across battery at 2000rpm (everything electrical switched on) _____13.94V
    5. Voltage at ALTERNATOR at 2000rpm (everything switched on)___________________
    6. Voltage drop between alternator body and battery negative (YES negative). Measure at max electrical load and 2000rpm ______________ (millivolts please)
    7. Voltage drop between alternator positive and battery positive. 2000rpm, max electrical load _____________
    8. Check Voltage drop from Battery Negative terminal to 1st groundpoint on vehicle_________0. 00V
    9. Check voltage drop from 1st ground point to block_____0.03V_____
    10. Check voltage drop from Alternator Housing to block__________

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