12V Battery VS Onboard Charger

[rx_for_assyria]

I need some advice on a puzzling issue with my 2019 Model S. The HV battery was replaced under warranty in 9/2023, followed by a 12V battery replacement in last month (12/2023) due to issues with not starting intermittently and the mobile service attributed to the 12V. Just after crossing 50,000 miles this month and exiting warranty, my car refused to go into drive, throwing codes and eventually blacking out of the blue.

Tesla roadside service pointed to a dead 12V battery, since it was recently replaced it would be covered under warranty. When it was towed, they did boost the battery and everything did seem to work. After diagnostics at Tesla, Tesla confirmed that the 12V battery is dead again and will be replaced under warranty, but they also found the onboard charger to be faulty, costing $3,000. I'm baffled because I never experienced any charging problems - at home or with superchargers.

Has anyone faced a similar situation or have insights on whether a faulty onboard charger could cause a 12V battery to die? Did the initial 12V battery failure that was replaced last month hint at this issue? Any advice would be greatly appreciated. Thanks!

 

[jdw]

On a 2019, the charger and the DC/DC converter are separate items. From 2021 all cars use a PCS (Power Control System) which contains the charger and the DC/DC converter.

As far as I know, if the charger had a problem, you'd have charging problems or at least limitations. If the separate DC/DC converter failed, that would lead to the 12v battery not charging. Sadly, the most common DC/DC failure is a blown fuse, which you can repair yourself, but it's not for the faint of heart.

This thread talks about the issues, and post 59 walks through a repair, but there have been three generations of DC/DC converters, and I believe you have a Gen 3 which is reportedly easier to repair, but I couldn't find much detail. The price you were quoted seems in the ballpark of what others were quoted. Hope this is some help.

DC - DC converter / AC compressor repair

Im still waiting for the fuse in the mail. I dont have anywhere around here that I could find what I needed, they should be here tomorrow, I will know tomrrow. I will be surprised if it doesnt fix the issues. If a fuse is all it takes to fix the AC compressor I am going to crap my pants...

teslamotorsclub.com

12 Volt Battery Compendium – TeslaTap

teslatap.com

 

[rx_for_assyria]

On a 2019, the charger and the DC/DC converter are separate items. From 2021 all cars use a PCS (Power Control System) which contains the charger and the DC/DC converter.

As far as I know, if the charger had a problem, you'd have charging problems or at least limitations. If the separate DC/DC converter failed, that would lead to the 12v battery not charging. Sadly, the most common DC/DC failure is a blown fuse, which you can repair yourself, but it's not for the faint of heart.

This thread talks about the issues, and post 59 walks through a repair, but there have been three generations of DC/DC converters, and I believe you have a Gen 3 which is reportedly easier to repair, but I couldn't find much detail. The price you were quoted seems in the ballpark of what others were quoted. Hope this is some help.

DC - DC converter / AC compressor repair

Im still waiting for the fuse in the mail. I dont have anywhere around here that I could find what I needed, they should be here tomorrow, I will know tomrrow. I will be surprised if it doesnt fix the issues. If a fuse is all it takes to fix the AC compressor I am going to crap my pants...

teslamotorsclub.com

12 Volt Battery Compendium – TeslaTap

teslatap.com

Super helpful. Really appreciate the insight.

So I had zero charging issues, yet they found a fault with the onboard charger. They never mentioned the DC/DC converter.

Based on your input, the 12V battery dying and the onboard charger are not related at all? Just want to make sure I'm understanding this correctly.

Attached is my invoice.

 

[jdw]

Sorry - gone for a few days ... I believe, but can't find confirmation, that the DC-DC converter on a 2019 S is a separate unit, unlike 2021+ cars, where it is combined in the charger. I can say that people who replaced the separate DC-DC converter, rather than repairing it paid around $2200 for it.

Unless you're doing the work yourself, Tesla *should* be quoting you on the cost to repair your car, whatever is wrong with it, so if they feel the problem is in the charger, you kind of have to go with that. It wouldn't hurt to ask about the DC converter being responsible for 12V charging, or ask how the charger affects 12V charging, just in case the repair doesn't fix the problem .... best of luck!

 

[philip295]

I need some advice on a puzzling issue with my 2019 Model S. The HV battery was replaced under warranty in 9/2023, followed by a 12V battery replacement in last month (12/2023) due to issues with not starting intermittently and the mobile service attributed to the 12V. Just after crossing 50,000 miles this month and exiting warranty, my car refused to go into drive, throwing codes and eventually blacking out of the blue.

Tesla roadside service pointed to a dead 12V battery, since it was recently replaced it would be covered under warranty. When it was towed, they did boost the battery and everything did seem to work. After diagnostics at Tesla, Tesla confirmed that the 12V battery is dead again and will be replaced under warranty, but they also found the onboard charger to be faulty, costing $3,000. I'm baffled because I never experienced any charging problems - at home or with superchargers.

Has anyone faced a similar situation or have insights on whether a faulty onboard charger could cause a 12V battery to die? Did the initial 12V battery failure that was replaced last month hint at this issue? Any advice would be greatly appreciated. Thanks!

My on board charger failed 2 years ago, Model S 2014 85s. I had the ccs upgrade at the same time (UK), £3,000