# Alert BMS_a305



## PiperPaul (Oct 31, 2018)

Can anyone clarify what this alert means? So far the local Tesla techs have told me "there is an external isolation and your vehicle may not restart". *Exciting*!
@Jason F : I see that you have been helpful on Alerts; hope you have some words of wisdom.


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## Ed Woodrick (May 26, 2018)

And what does Tesla say to do?


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## PiperPaul (Oct 31, 2018)

Ed Woodrick said:


> And what does Tesla say to do?


So far, bring it in for service. However, it may not restart at any time based on the active BMS readings, so if it will allow moving into Drive then it may not run again after leaving gear.
In other words: if I'm lucky I can drive it to the Service Centre (without any stops), otherwise it becomes a conversation piece in my garage.

What I've found so far is that this all relates to eliminating the chance that high voltage jumps to the car chassis. If the BMS allows the motors to engage (Drive, Reverse) then it monitors the situation and decides the risk for the next instance. I.e.: How lucky do you feel?


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## Ed Woodrick (May 26, 2018)

PiperPaul said:


> So far, bring it in for service. However, it may not restart at any time based on the active BMS readings, so if it will allow moving into Drive then it may not run again after leaving gear.
> In other words: if I'm lucky I can drive it to the Service Centre (without any stops), otherwise it becomes a conversation piece in my garage.
> 
> What I've found so far is that this all relates to eliminating the chance that high voltage jumps to the car chassis. If the BMS allows the motors to engage (Drive, Reverse) then it monitors the situation and decides the risk for the next instance. I.e.: How lucky do you feel?


My thoughts are that if Tesla thought that it was dangerous, then they'd just cut the car off. I'd get in into service ASAP. And if it doesn't run when you get it there, it's in the right place.


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## PiperPaul (Oct 31, 2018)

Ed Woodrick said:


> My thoughts are that if Tesla thought that it was dangerous, then they'd just cut the car off. I'd get in into service ASAP. And if it doesn't run when you get it there, it's in the right place.


Thanks Ed. That is my current plan although the first appointment available is next Tuesday.


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## PiperPaul (Oct 31, 2018)

PiperPaul said:


> Thanks Ed. That is my current plan although the first appointment available is next Tuesday.


*Update*: 
Now that I have installed 2022.24.8 all Notifications and Alerts have disappeared. (Seems the update has simply cleared the data.)
BUT when I checked about that with the Service Centre they recommended I monitor the car over the weekend. 
Hmmm. 

Remote diagnostics indicated a problem. 
Driving the car may result in a no-restart. 
Now I should drive the car and see if I get a new Alert?
This seems like a sketchy plan. How lucky do I feel?


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## JasonF (Oct 26, 2018)

PiperPaul said:


> Can anyone clarify what this alert means? So far the local Tesla techs have told me "there is an external isolation and your vehicle may not restart". *Exciting*!
> @Jason F : I see that you have been helpful on Alerts; hope you have some words of wisdom.


If everything is working - car driving, HVAC cooling, etc - it's probably the 12V battery going out. See if Service agrees and can expedite the 12V replacement, and meanwhile Keep Climate On for a while when you're out and about. If they don't agree and nothing bad happens for a week or so, it might have just been a temporary 12V voltage drop.


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## PiperPaul (Oct 31, 2018)

JasonF said:


> If everything is working - car driving, HVAC cooling, etc - it's probably the 12V battery going out. See if Service agrees and can expedite the 12V replacement, and meanwhile Keep Climate On for a while when you're out and about. If they don't agree and nothing bad happens for a week or so, it might have just been a temporary 12V voltage drop.


Thanks Jason. 
Tesla Service says "there is an isolation present" according to their remote diagnostics. If this means what I've read elsewhere that the high voltage system is no longer properly isolated then it sounds more complicated than the 12V battery. 
BUT I don't have a comfort level from their messages that they are really sure, so appreciate your thoughts.


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## JasonF (Oct 26, 2018)

PiperPaul said:


> Thanks Jason.
> Tesla Service says "there is an isolation present" according to their remote diagnostics. If this means what I've read elsewhere that the high voltage system is no longer properly isolated then it sounds more complicated than the 12V battery.
> BUT I don't have a comfort level from their messages that they are really sure, so appreciate your thoughts.


An isolation present might just mean one of the auto reset circuit breakers tripped.

The high voltage and drive systems are _really_ simple. If you lose any portion of it, you won’t be able to move the car, or you won’t have HVAC, or the car won’t charge, or the 12V battery will go flat from lack of charging. In any case you’ll know very quickly if something in it fails.

If it’s not obvious what this “isolation” is, it’s more than likely on the 12V side**. But if the MCU works, and you can hear the cooling fans run, and the coolant pump circulates, and the contactors close, and the exterior lights all work, it’s something to get fixed but not to be worried about.

By the way, a dead cell developing in the 12V battery will cause an “isolation” event because it will create a short circuit.

** - If you have an older model with resistive heating, it’s possible for it to blow its fuse and disconnect from the high voltage side without affecting any other systems. But once again, something to fix but not be worried about.


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## PiperPaul (Oct 31, 2018)

JasonF said:


> An isolation present might just mean one of the auto reset circuit breakers tripped.
> 
> The high voltage and drive systems are _really_ simple. If you lose any portion of it, you won’t be able to move the car, or you won’t have HVAC, or the car won’t charge, or the 12V battery will go flat from lack of charging. In any case you’ll know very quickly if something in it fails.
> 
> ...


Okay; thanks Jason.
I do have an older model: 2018 Long Range AWD with resistive heating. 
And all systems appear to be working normally. 
And the 12V Battery is the original, so a strong possibility for replacement.

Just moved the car to see what happens and everything seems normal AND no alerts or notifications. So I'll use it this weekend and see what happens. I'll also turn on the heating to see if that is OK.

Coincidentally, the Streaming service is having problems. Left along it seems to not be able to connect to play music. After I switch to a radio station and then back it is fine. Not nearly a serious as the car not running. Weird week!


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## PiperPaul (Oct 31, 2018)

PiperPaul said:


> Okay; thanks Jason.
> I do have an older model: 2018 Long Range AWD with resistive heating.
> And all systems appear to be working normally.
> And the 12V Battery is the original, so a strong possibility for replacement.
> ...


Also: Would a voltage meter on the 12V tell me anything useful about the battery condition?


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## JasonF (Oct 26, 2018)

PiperPaul said:


> Also: Would a voltage meter on the 12V tell me anything useful about the battery condition?


It will tell you if the voltage is low, but it won't really help with a dying cell condition.


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## PiperPaul (Oct 31, 2018)

JasonF said:


> It will tell you if the voltage is low, but it won't really help with a dying cell condition.


Thanks.
After a day of no alerts I am now getting a new one: Vcfront_a192 which leads to an Owners Manual entry indicating the 12 V battery as you first said. So my next step is to find the appropriate battery locally.


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## JasonF (Oct 26, 2018)

PiperPaul said:


> Thanks.
> After a day of no alerts I am now getting a new one: Vcfront_a192 which leads to an Owners Manual entry indicating the 12 V battery as you first said. So my next step is to find the appropriate battery locally.


If you can get them scheduled, Tesla mobile service installs those for $129.


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## PiperPaul (Oct 31, 2018)

JasonF said:


> If you can get them scheduled, Tesla mobile service installs those for $129.


Yes; I'm also trying to change my Service Centre appointment to have my usual Mobile Rep come with a replacement.
There are many posts about this being a Warranty item so I've asked re: my appointment if this is the case.
Would save me a half day of travel etc. even if they are going to charge me.

It's not clear if this is a Warranty item. I'm not expecting it is after 4 years but my Basic Warranty expires this November. So I'll see what they say.


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## PiperPaul (Oct 31, 2018)

PiperPaul said:


> Yes; I'm also trying to change my Service Centre appointment to have my usual Mobile Rep come with a replacement.
> There are many posts about this being a Warranty item so I've asked re: my appointment if this is the case.
> Would save me a half day of travel etc. even if they are going to charge me.
> 
> It's not clear if this is a Warranty item. I'm not expecting it is after 4 years but my Basic Warranty expires this November. So I'll see what they say.


Short update:
Tesla Service says I still have to take the car in for the isolation fault regardless of the change in error messages.
No reply on the 12V battery being under warranty or not.
If you don't hear from me after noon tomorrow I'll be at the side of the highway to Halifax hitching a ride.


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## PiperPaul (Oct 31, 2018)

Final update:
Got the car to the Halifax (Bedford) Service centre Tuesday with no trouble (and no hitch hiking). Had to wait 3 hr. for a loaner M3 to be returned by a customer while the Techs ran diagnostics. Got home Tuesday evening with really no information about the car's status. Notified this afternoon (Wednesday) the car was ready - still in the dark after 24 hrs.

However; I did bump into the Technician who had worked on the car just before I brought it home and discovered:

there was a high voltage isolation fault due to the rear drive inverter (so he said I *was* lucky the car didn't quit on me)
the inverter was replaced - this required dropping the whole rear drive assembly: wheels, suspension, motor, etc.
apparently this problem has been seen before, and he said something about a grounding strap becoming corroded 
with the rear suspension removed he also found worn bushings on the upper forward and rear links on both sides which he replaced
he said he was in the shop from 5 am. to do all this after the previous day's diagnostics
Setting aside the original wait and lack of communication, I was impressed that they got all that done relatively quickly and at no charge.
Oh; and a new 12V battery installed for good measure, again covered by the warranty.
All's well that ends well.


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