Dead Model 3 12V Battery: HV Isolation Issue and 1400$ charge to fix?

[evildede]

First time posting here. I've had my Tesla Model 3 SR+ Since July of 2019 and got the notification that my 12V battery was dying on December 31. I went to the car and couldn't get in, battery was dead.

Messaged Tesla for a mobile servicing of the battery, was given a date of January 8. Messaged again to say it was unacceptable as I needed the car and it was in a unusable state, and they they told me the car needed to be brought in to check on an High Voltage isolation issue that drained the battery, which to me is weird as the 12V battery lasted me 4 and a half years when apparently it should die after 3, so I doubt it was due to heavy drainage.

Got the car towed in Tesla due to the job being done tomorrow morning. They then added a 420$ diagnostic cost which I had to accept after they told me it was normal due to them having to confirm that there isn't any issues there before changing the 12V battery. I accepted the estimate, which was a bit above 600$ CAD by then.

Not even 5 minutes after I approve that estimate, I get sent another one asking above 1400$ yet and to approve estimate before they can get working on my car, yet as far as I can see Service Center was about to close and my car hasn't been touched according to the Tesla app and is scheduled for tomorrow morning at 10:00.

When we jump started the car to put it in tow mode, the only error message I had was ''12V Battery dead, car might not start again if shut down''. Being the first time it happened and hearing that the 12V battery replacement is apparently not expensive, plus the fact I get free towing with insurance and not having a second car around right now, I though it made sense to let Tesla do it. Now I'm on the hook for more than 1400$ for what seemed like such a small issue and I really don't understand why, especially since if they find no issues I'll still have to pay the diagnostic fees as per their message.

Is this normal coming from them? Has this happened to anyone else before?

 

[Tam]

First time posting here. I've had my Tesla Model 3 SR+ Since July of 2019 and got the notification that my 12V battery was dying on December 31. I went to the car and couldn't get in, battery was dead.

Messaged Tesla for a mobile servicing of the battery, was given a date of January 8. Messaged again to say it was unacceptable as I needed the car and it was in a unusable state, and they they told me the car needed to be brought in to check on an High Voltage isolation issue that drained the battery, which to me is weird as the 12V battery lasted me 4 and a half years when apparently it should die after 3, so I doubt it was due to heavy drainage.

Got the car towed in Tesla due to the job being done tomorrow morning. They then added a 420$ diagnostic cost which I had to accept after they told me it was normal due to them having to confirm that there isn't any issues there before changing the 12V battery. I accepted the estimate, which was a bit above 600$ CAD by then.

Not even 5 minutes after I approve that estimate, I get sent another one asking above 1400$ yet and to approve estimate before they can get working on my car, yet as far as I can see Service Center was about to close and my car hasn't been touched according to the Tesla app and is scheduled for tomorrow morning at 10:00.

When we jump started the car to put it in tow mode, the only error message I had was ''12V Battery dead, car might not start again if shut down''. Being the first time it happened and hearing that the 12V battery replacement is apparently not expensive, plus the fact I get free towing with insurance and not having a second car around right now, I though it made sense to let Tesla do it. Now I'm on the hook for more than 1400$ for what seemed like such a small issue and I really don't understand why, especially since if they find no issues I'll still have to pay the diagnostic fees as per their message.

Is this normal coming from them? Has this happened to anyone else before?

$600 or $1,400 is just plain crazy.

If you are handy, you can buy a new 12v battery from Service Center and install it yourself. You can watch YouTube for instructions.

If that doesn't fix the car then paying additional money to Tesla is reasonable.

 

[evildede]

So they did the work this morning and indeed charged 1400$. They say they saw a small isolation issue that resolved in small heat loss and had the change the PTC heater for a grand total of 1489$ CAD. I’m heading there to see why as my 12V battery lasted 4.5 years and my cabin heating has always been fine so I really don’t understand why that was done to my car when all I wanted in the beginning was a 12v battery change.

 

[m73b54]

You should just replace that stupid $100 battery first and see what will happen.

 

[Tam]

So they did the work this morning and indeed charged 1400$. They say they saw a small isolation issue that resolved in small heat loss and had the change the PTC heater for a grand total of 1489$ CAD. I’m heading there to see why as my 12V battery lasted 4.5 years and my cabin heating has always been fine so I really don’t understand why that was done to my car when all I wanted in the beginning was a 12v battery change.

It's true to cost more for the heater but like you said, it's been working fine!

The heater doesn't use 12v. It uses high voltage from the main battery pack.

You should have watched YouTube and changed the 12v yourself.

 

[GtiMart]

It might be two unrelated issues: your 12V dying and separately your PTC heater having an issue that they fixed preemptively. If I read your message correctly, the PTC was pulling power even when not in use or something like that. You are correct, the PTC runs on the HV and not the 12V.

 

[evildede]

It might be two unrelated issues: your 12V dying and separately your PTC heater having an issue that they fixed preemptively. If I read your message correctly, the PTC was pulling power even when not in use or something like that. You are correct, the PTC runs on the HV and not the 12V.

They said it had to do with the high voltage battery and that they tested to make sure before changing the part and after and that the error message is now gone after the change.
I’ll be honest I do see a difference with the heating, however I don’t know if they really needed to do that work now and just preemptively did it and if it could have lasted a bit more. Considering it affected the high voltage battery and that I don’t want that to fail on me I guess it’s a good thing they did it. Just didn’t expect such an expensive repair so early on the car and just barely out of warranty…

 

[Tam]

They said it had to do with the high voltage battery and that they tested to make sure before changing the part and after and that the error message is now gone after the change.
I’ll be honest I do see a difference with the heating, however I don’t know if they really needed to do that work now and just preemptively did it and if it could have lasted a bit more. Considering it affected the high voltage battery and that I don’t want that to fail on me I guess it’s a good thing they did it. Just didn’t expect such an expensive repair so early on the car and just barely out of warranty…

12v is cheap. Heater is expensive.

 

[evildede]

12v is cheap. Heater is expensive.

yup, 12v, with the work, was like 165$ CAD. Battery itself is 120$ CAD, so the bulk of the fix was the heater.

 

[dbeiler]

All high voltage components in electrified vehicles are regularly monitored for isolation faults via onboard hardware/software. Isolation tests are necessary for safety reasons. Insulating materials in the high voltage components break down over time due to various reasons. Humans do not survive being subjected to 400vdc from a battery pack.

Here is what most likely happened to your vehicle:
At some point after you exited the vehicle, an isolation fault was detected in the PTC heater.
The vehicle high voltage contacts were commanded open. This disconnects the high voltage battery from the rest of the vehicle, keeping the occupants safe until the isolation fault is repaired.
Because the high voltage battery was disconnected, the 12V battery was no longer being charged.
The 12V battery drained until it died.
A new 12V battery might have survived a deep-cycle drain. An older battery will not. One deep-cycle drain will be the straw that breaks the camels back.

Had you replaced only the 12V battery, the car would still be broken. The vehicle will not close the high voltage contacts if an unsafe isolation fault still exists.

 

[evildede]

All high voltage components in electrified vehicles are regularly monitored for isolation faults via onboard hardware/software. Isolation tests are necessary for safety reasons. Insulating materials in the high voltage components break down over time due to various reasons. Humans do not survive being subjected to 400vdc from a battery pack.

Here is what most likely happened to your vehicle:
At some point after you exited the vehicle, an isolation fault was detected in the PTC heater.
The vehicle high voltage contacts were commanded open. This disconnects the high voltage battery from the rest of the vehicle, keeping the occupants safe until the isolation fault is repaired.
Because the high voltage battery was disconnected, the 12V battery was no longer being charged.
The 12V battery drained until it died.
A new 12V battery might have survived a deep-cycle drain. An older battery will not. One deep-cycle drain will be the straw that breaks the camels back.

Had you replaced only the 12V battery, the car would still be broken. The vehicle will not close the high voltage contacts if an unsafe isolation fault still exists.

Very insightful! You actually did a better job than the people at the service center explaining this to me!

 

[Ti317]

Putting things in perspective, the $1400 CAD after almost 5 years of ownership is less than the cost to replace one fuel injector in a similar sports sedan like a BMW 3 Series.
It’s not like anyone would be eager to shell out cash needlessly but this is not an unreasonable expense of ownership IMO.

 

[evildede]

Putting things in perspective, the $1400 CAD after almost 5 years of ownership is less than the cost to replace one fuel injector in a similar sports sedan like a BMW 3 Series.
It’s not like anyone would be eager to shell out cash needlessly but this is not an unreasonable expense of ownership IMO.

I was used to a Toyota Corolla, which I still own, and has had 0 work on except for breaks and oil changes, after now 11 years. I also had other little things done on the Tesla and now more problems are coming out. Like, I love the car, just not used to having to spend this much for repairs after less than 5 years.

 

[Ti317]

I was used to a Toyota Corolla, which I still own, and has had 0 work on except for breaks and oil changes, after now 11 years. I also had other little things done on the Tesla and now more problems are coming out. Like, I love the car, just not used to having to spend this much for repairs after less than 5 years.

You were spoiled. Any performance/luxury sports car is going to be higher maintenance. As a BMW and Audi owner for a few decades, I already factor in the higher cost of ownership

 

[newhus]

How is your car now? I had the exact same problem. Car bricked itself overnight last December during a software update. Tesla had it for 3 weeks, and the 12v was replaced twice.

In February it bricked itself again in my driveway at night. Towed again. This time they claimed it was the ptc heater which cost $1300.

Went to pick up the car and it was bricked overnight at the service center!

Today they said they replaced the 12v for the 4th time, and they claim somebody at the service center left the door open, killing the brand new battery (#4).

 

[Ti317]

How old is your car? Is there no warranty coverage left?
Not sure how CA laws are but I would start by contacting your department of consumer affairs or its equivalent.
I’m not buying their story. Every car that I’ve own that was made in this century would go to sleep if the doors or trunk were left open for too long.

 

[newhus]

It was purchased July 2019, so 4.5 years. It has 24,000 miles on it.

I can’t believe they said the reason the battery failed was a tech left the door open. We will see, but if it fails again I believe it could trigger a California Lemon Law.

I have to say not one person has apologized for it failing 3 times, or even my going to pick it up to find the alert still there in their parking lot. Not the best customer service.

 

[Ti317]

It was purchased July 2019, so 4.5 years. It has 24,000 miles on it.

I can’t believe they said the reason the battery failed was a tech left the door open. We will see, but if it fails again I believe it could trigger a California Lemon Law.

I have to say not one person has apologized for it failing 3 times, or even my going to pick it up to find the alert still there in their parking lot. Not the best customer service.

Not sure how California does Lemon Law but other than the age it seems like a prime candidate.
I know Tesla is a different business model but I have had very good results over the years with BMW by going directly to the head office.
A call to corporate may yield results even now. Start by outlining your story and ask if there is any room for a goodwill adjustment? If they say they will look into it, give them some time to make it right. Usually there will be a check in the mail in 2 weeks.
If they reject you out of hand, say that this may be a good story for your local TV station’s consumer help line and it’s not like EVs need any more negative press.
Good luck with it. I’m placing a prop bet that it recurs in less than a month.