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Discussion Starter #1
2013 Evoque dynamic, thru this fault 2 weeks ago. After a week, I put in a new AGM battery. Week 2, fault still there...
Car is charging fine....old and new battery turned over fine, even in -20C temps.
Metering the BMS fusable wire link from ground to battery + shows just 11.4V...
Same wire to positive side shows full battery voltage, measured from battery ground.
The battery monitoring system is a part of the battery ground lug. Is that 11.4V low? Should it be same as battery voltage? Perhaps its bad...?

20190123_121233.jpg .
 

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11.4 is very low. You may have a cable with high resistance not allowing the alternator to fully charge the battery. You could also a loose or corroded connection.
 

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Discussion Starter #3
Battery voltage and alternator charge voltage is good. The fused link cable ground to positive is the one reading 11.4V
For testing, I measure the resistance of the bms harness....its okay.

Had LR plug into the ECU and it had a B11DB-87 code stored. All they told me is they would have to start checking all the wiring at a minimum of 5 hrs service charge!
Everything Ive read about this code points to the BMS monitor itself (attached to the battery)
Harness wires dont show open circuit for power...Im unsure what the LIN is spose to show for V, if any...?


11.4 is very low. You may have a cable with high resistance not allowing the alternator to fully charge the battery. You could also a loose or corroded connection.
 

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So, JUST put in a new BMS module... Warning is still there, however it MAY need time to recalibrate... Or may need reset?
If not, I have no clue where to look next.

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Have you checked your other cables and grounds for clean tight fitting? You are skipping the easy stuff.

No matter what you say, 11.4v is very low at any point in start/charge circuit.
 

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Discussion Starter #6
Have you checked your other cables and grounds for clean tight fitting? You are skipping the easy stuff.

No matter what you say, 11.4v is very low at any point in start/charge circuit.
I checked the continuity and resistance of the fused Connector from the BMS to the positive terminal. It's okay...
11.4V is from the positive battery post to the BMS itself, measured thru the fused Connector, as this is the + path for the BMS. I'm assuming the BMS has some internal resistance to calculate voltage...?
Same voltage on new and old BMS by the way.
The ground post connection is solid according to my measurements... So my assumption is ground point to negative post is also good.
Also, still 13.9V at battery while idling. Assuming thats a good alternator voltage, nothing amiss there.

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Discussion Starter #7
I guess I'll start checking connections at the other end of all these cables... The LIN conductor to the BCM and ground connections.

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So, JUST put in a new BMS module... Warning is still there, however it MAY need time to recalibrate... Or may need reset?
If not, I have no clue where to look next.

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what model year? my '17 kept throwing charging errors and low battery alarms.
there was nothing wrong with either the charging or the battery, the car needed a software update.
 

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Discussion Starter #9
what model year? my '17 kept throwing charging errors and low battery alarms.
there was nothing wrong with either the charging or the battery, the car needed a software update.
Mines a 2013...
Was at the dealer and plugged in. Didn't receive an update.

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Try this: Start the vehicle, and check the voltage between the positive connection to the battery and the positive connection to the BMS. Also check the voltage between the ground and the battery negative. Both should measure less than .3 volts. Much more than that indicates a voltage drop. This system uses SYSTEM voltage to indicate battery voltage, and it will assume that the voltage is low if it "sees" a low voltage at the measurement point. Let me know... Ray
 

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Discussion Starter #11
Try this: Start the vehicle, and check the voltage between the positive connection to the battery and the positive connection to the BMS. Also check the voltage between the ground and the battery negative. Both should measure less than .3 volts. Much more than that indicates a voltage drop. This system uses SYSTEM voltage to indicate battery voltage, and it will assume that the voltage is low if it "sees" a low voltage at the measurement point. Let me know... Ray
I see what you're saying...
See if there is any potential difference at these points. Good idea...
This should reveal any bad or corroded connections.
Thanks....
I'll report back.

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Discussion Starter #12
I did measure battery ground post to BMS + Connector and it was less than 12V. Both with the old and new BMS.
This may be a normal voltage for the BMS... Can't be sure unless someone else measures this on their vehicle.

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Discussion Starter #13
One important connection I failed to meter was the + that connects to the BMS fused link. Mainly because I couldn't get my meter probe into the female plug end...
This lead doesn't come straight off the positive battery post (that I could see) so maybe the issue lies here. Would be an easy fix if this were it.
If the issues is with the LIN line, it'll be a major PITA as it ends up on the BACK side of the fuse block behind the glove box.
 

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Suggestion: can you measure the voltage drop between the battery and the monitor connection to the module? If that fuse is blown, the voltage between these points will be quite high. Typically this fuse blows when the alternator fails, causing faults, even though the system is charging properly. I would check this first. It might save you some headaches. Ray
 

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Suggestion: can you measure the voltage drop between the battery and the monitor connection to the module? If that fuse is blown, the voltage between these points will be quite high. Typically this fuse blows when the alternator fails, causing faults, even though the system is charging properly. I would check this first. It might save you some headaches. Ray
Fused link is intact... Measured continuity thru it. Plus it's brand new.
I have to find time to measure the positive voltage feeding the BMS, and any potential loss to ground or from alternator.
Measuring the voltage from ground to the + at the BMS, shows 11V however.
I think this must be by design, as my old and new BMS measured the same.
 

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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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Discussion Starter #17
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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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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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
 

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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
 
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