New Tesla Owner w/ Dead 12v + maybe dead DC-DC Converter?

[orccro]

I recently bought a 2019 Model S Performance. Car seemed good, test drove well, no errors or problems. Took ownership then went and charged it up before heading home with the new (to me) car. Car was parked at my home with about 75% SOC, everything seemed normal. I decided to perform an update from 2023.20.9 -> 2023.44.30.8.

The car reported the download successful and was installing but never got past 80% installation. After waiting a couple hours I went to check the car and found it to have very low power. The doors were not opening correctly and the MCU/dash were black. I released the frunk manually and got to the LV battery which was at about 5volts, so very drained.

Next day I visited a tesla service center and got a new battery, same as the old one. Put the new battery in, car makes some noises and comes back to life. The car had a lot of error messages, and wanted to finish the update before driving, so I resumed the installation which picked up at 80% where it previously stopped. But it never made progress, it stayed at 80% until this brand new battery also had voltage drop, down to about 11.4, at which point the MCU died again (doors/lights still functioned, the voltage did not get as low as previous).

This seems like a dead DC-DC converter from what I can gather. The HV battery would display a good amount of power when the LV battery had power to run the display, but the LV battery is not being sustained. If not a bad DC-DC converter then maybe related to the software installation being stuck? Does the installation temporarily override the DC-DC conversion process?

Any suggestions would be appreciated. Thanks

 

[ewoodrick]

Did you tell the Service Center to just replace the battery or did you ask them to diagnose it?

 

[orccro]

I had went and purchased the new battery on my own without a diagnosis from any Tesla employees.

 

[ewoodrick]

I had went and purchased the new battery on my own without a diagnosis from any Tesla employees.

Recommendation: Always have the charging system checked on ANY vehicle before changing a battery. Unless you are changing for preventative maintenance.

I can't tell you the number of ICE owners that I've seen replace the battery on a car with a dead alternator.

 

[ATPMSD]

Something to check, which is a shot in the dark. When replacing the 12v battery, part of the procedure is to disconnect the HV loop, did you reconnect it after installing the battery?

If you think the DC/DC convert has failed, use another 12v battery to jump the one in the car. When the car wakes up, step on the brake, you should hear a solid click, which should be the contractor closing.

You can also put the car into “Service Mode,” there is a menu item to look at the batteries and I am pretty sure you will be able to see if HV battery is powering the LV bus.

Good luck!

 

[orccro]

Recommendation: Always have the charging system checked on ANY vehicle before changing a battery. Unless you are changing for preventative maintenance.

I can't tell you the number of ICE owners that I've seen replace the battery on a car with a dead alternator.

Yes, good advice.

It seems either the software installation hanging at 80% has prevented the 12v battery from being maintained correctly or the dcdc converter just happened to coincidently fail during the update.

Something to check, which is a shot in the dark. When replacing the 12v battery, part of the procedure is to disconnect the HV loop, did you reconnect it after installing the battery?

If you think the DC/DC convert has failed, use another 12v battery to jump the one in the car. When the car wakes up, step on the brake, you should hear a solid click, which should be the contractor closing.

You can also put the car into “Service Mode,” there is a menu item to look at the batteries and I am pretty sure you will be able to see if HV battery is powering the LV bus.

Good luck!

I did disconnect the HV loop during the new battery's installation and have since reconnected it. But I will check this connector to ensure it is making correct contact.

For the jump process, should this be done from a running car or while the donor car is off?

I have attempted to get into service mode, but now that both battery's have lower power I do not have much time to interact with the MCU/dash before I get a "standby..." message and it crashes. But I will try the jumper method and that should give me more time. But I do not believe the HV is powering the LV bus. I was just able to get into service and take a picture of the errors before an MCU crash, image quality not great but it was in a rush. The HV battery seems to be having trouble. But I think those errors are likely to go away, because the everything has been working well just before the update attempt, and even after the first failed update the new battery keep the system running for about an hour or two while stuck installing and in that period I could see on the app the reported battery SOC increase from an initial 0% up to the expected 75% before battery power and app readings were again lost.

 

[orccro]

Well for what it is worth to anyone else out there with a similar issue my problem ended up being a dead HV battery. Ultimately had the car towed to a Tesla service center and the HV battery (and dead LV) were replaced under warranty.

This is on a 2019 Performance (raven) with 57,000 miles.

 

[Bigriver]

Ultimately had the car towed to a Tesla service center and the HV battery (and dead LV) were replaced under warranty.

Hurray for the warranty!!