Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

12V issue and "isolation"

cpa

Active Member
May 17, 2014
3,160
4,112
Central Valley
Well, I got the dread "12V error warning" earlier today as I got back into my car to return home from the grocery store. It cautioned me that my car may not restart. It took a few moments, but I was able to put the shift lever in drive, and I made it home.

I telephoned roadside assistance, and they told me that Seaside Service Center would be contacting me no later than Monday.

The service manager from Seaside called me about 45 minutes later. I inquired if the ranger could just come to Fresno when convenient next week to replace the 12V. He indicated that after he pulled my logs that there was a more serious (but not horrible) issue with "battery isolation." He apologized that he was not as familiar with the logs as the technicians are, but he felt that it had something to do with the battery heater.

(I told him that I thought something may be a little off, as the notification that I receive upon completion of charging would indicate that the battery was at 202RM, but when I would enter the car a few hours later, the rated miles were always down to around 192-194.) That seemed highly odd, as the lows here are not that terribly low (probably 45 degrees in the garage.)

So, the S85 will be picked up Wednesday morning and hauled to Monterey/Seaside.

Finally, what is interesting is that the return e*mail address refers to [email protected] However, apparently that address has not been created formally, as when I replied to the calendar appointment to thank them for prompt service, it was returned. (And yes, I just used the blue underlined link in the email that Tesla generated to me.)

Has anyone else experienced this sort of issue with the battery heater?
 

Ingineer

Electrical Engineer
Aug 8, 2012
1,507
3,699
To my knowledge, there is is no way a high-voltage isolation fault can be traced to a particular component automatically be the car.

If the car detects an isolation fault, it may refuse to close the main contactor. If that happens, the DC-DC converter will not be powered and the car will issue the 12v system warning. Apparently the isolation fault must have cleared and the BMS finally closed it's contactors, otherwise you wouldn't have been able to drive.

For those that don't know, the high-voltage system is totally isolated from the chassis, and the BMS is constantly checking for leakage current to/from the high voltage system and the chassis. In the event the leakage current exceeds a certain threshold, it will indicate a fault and may lock out high-voltage power on start up. This is done for safety.

If the battery heater did have an insulation fault there is no real way for the car to know , and it would be up to the technicians to locate the fault by disconnecting parts of the system and measuring it until the find the leak.
 

Ingineer

Electrical Engineer
Aug 8, 2012
1,507
3,699
I'm not (yet) sure exactly how Tesla does it, but it will involve checking resistance from each side of the pack to chassis and looking for leakage. The Prius did this with a square wave alternating between pack plus/minus and watching for current flow over a set threshold. I think the Tesla system also does some kind of a pre-closure check as well. This is all done inside the pack's sealed housing, so in the event of a fault, no high-voltage will come out of the pack.

It works almost like a GFCI (RCD) does on AC power.
 

cpa

Active Member
May 17, 2014
3,160
4,112
Central Valley
I'm not (yet) sure exactly how Tesla does it, but it will involve checking resistance from each side of the pack to chassis and looking for leakage. The Prius did this with a square wave alternating between pack plus/minus and watching for current flow over a set threshold. I think the Tesla system also does some kind of a pre-closure check as well. This is all done inside the pack's sealed housing, so in the event of a fault, no high-voltage will come out of the pack.

It works almost like a GFCI (RCD) does on AC power.

Thanks for your explanation! I will update this thread as I receive information from service.
 

cpa

Active Member
May 17, 2014
3,160
4,112
Central Valley
Here is the description per the invoice from Tesla Service:

Concern: Customer states Alert appeared: "Car Needs Service, Car May Not Restart", car
can restart.
Pay Type: Warranty
Corrections: Vehicle Alerts General Diagnosis
Pulled vehicle logs and found alerts for internally faulty battery coolant heater. Replace
coolant heater and re-check.
Corrections: Coolant Heater - Electric - Battery - 2nd Generation
Removed and replaced electric battery coolant heater. Verified no alerts present at this
time and vehicle is operating optimally.
Part Quantity
ELECTRIC BATTERY HEATER - RWD AND
DUAL MOTOR (1038901-00-G)
1
ETHYLENE GLYCOL COOLANT - 50/50 MIX
- 1 gallon (1029320-00-A)
1
Parts Replaced or Added
0.00
RONC9714000352

Apparently the battery heater was not operating properly from time-to-time. This conclusion was derived from the diagnostics that service received on my car. The way that I understood the service technician was that this error message is rather general instead of specific. Any sort of issue that concerns the main pack generates this sort of warning, as there could be much more serious problems which would cause the car to shut down permanently.
 

Kalud

Active Member
May 7, 2013
1,059
290
Montreal, QC
I did not know there was a separate battery heating module.

Yes, Battery heater (coolant), Battery chiller (shared with cabin) acting on coolant, and cabin air heater.

Temp Screen 5.12.JPG
 

Atebit

Member
Jan 7, 2014
286
26
PA
Same thing happened to me while charging at the Glen Allen SC last May. Tesla had to flatbed the car back to NC and gave me a loaner car to continue our trip to PA & back to NC again. Bad timing all around :)
 

GoBlue88

Member
Apr 1, 2014
853
263
Carlsbad, CA
Same thing happened to me while charging at the Glen Allen SC last May. Tesla had to flatbed the car back to NC and gave me a loaner car to continue our trip to PA & back to NC again. Bad timing all around :)
Have you had any related issues since they replaced the coolant heater unit? I'm hoping this doesn't happen again.
 

GeorgeCM

Member
Mar 18, 2017
65
63
Europe
Hi guys,
Got almost the same isue, 12v battery discharged, car does not drive, contactors don't close. I suppose there is an isolation issue. I can see in BMS data isolation res. 3580 kOhms, which looks normal. I suppose this is internal isolation.
To my knowledge, there is is no way a high-voltage isolation fault can be traced to a particular component automatically be the car.

If the car detects an isolation fault, it may refuse to close the main contactor. If that happens, the DC-DC converter will not be powered and the car will issue the 12v system warning. Apparently the isolation fault must have cleared and the BMS finally closed it's contactors, otherwise you wouldn't have been able to drive.

For those that don't know, the high-voltage system is totally isolated from the chassis, and the BMS is constantly checking for leakage current to/from the high voltage system and the chassis. In the event the leakage current exceeds a certain threshold, it will indicate a fault and may lock out high-voltage power on start up. This is done for safety.

If the battery heater did have an insulation fault there is no real way for the car to know , and it would be up to the technicians to locate the fault by disconnecting parts of the system and measuring it until the find the leak.
It seams that BMS measures separate internal and external insulation. I have external insulation alert. However, BMS shows a good value for insulation, I suppose that one is internal as in the below pictures. Any idea if measuring the resistance between + and chassis respective - and chassis of each of the suspected high voltage components is the way to go ? I suppose values above 2000-3000 Kohms should be considered good insulation ?

IMG_20190701_153843.jpg
IMG_20190701_195610.jpg
 

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top