Working on your car can be dangerous. Working on an electric vehicle can also be dangerous - made worse by the fact that high voltage isn't fully understood by many otherwise competent mechanics and DIY enthusiasts. The content on this page is for informational purposes only. Readers agree to follow all safety recommendations and assume any/all risk.
This website discusses the High Voltage Battery packs used in 2012-2020 Tesla Model S and Model X vehicles. It is organized in sections with menus that are easier to navigate and read on a desktop browser. If your car recently shut down and you believe the HV Battery is the cause, the information here is intended to point you in the right direction to ask the right questions of a shop or towards a DIY repair if you have the skills, time and ambition. If your pack just died a minute ago, you can skip ahead to some preliminary things you need to do to help your 12V battery survive the process. When the HV battery dies there are several, sometimes dozens of errors that populate the screen. In that condition, the HV battery doesn't charge/support the 12V battery even though most of the other systems (like the computer/MCU screen) keep running so most of the errors are related to the 12V going dead. Most of the errors listed have nothing to do with the primary malfunction. One short-term goal is to keep the 12V alive long enough to identify the errors and read some of the battery information with a tool called Scan My Tesla so we have an educated guess about what is wrong. You will also want to snap pictures of the errors to help with the diagnosis - preferably from Service Mode. For some of the troubleshooting, the forums and Facebook groups will be your best resource. After that, this guide will provide some step-by-step for the actual repair. I know you will skip around a lot, but please come back and read EVERYTHING before you start any repairs - especially the extensive safety warnings below.
I'm just a guy who likes tinkering and fixing my own things. When I bought a Tesla Model S, it was awesome until the HV battery died 6 months later. Like most things, I decided to fix it myself despite ZERO go-to repository for information. I hope this helps others keep their cars on the road too. Even if you never touch a bolt on the car, this information will help you understand the process, make the correct requests of, and ask the right questions of the shop you choose to have work on the battery. If you are considering buying one of these early Teslas, perhaps the information here will give you confidence or alternatively, cause you to steer a different direction. Some people shouldn't own any car out of warranty. Some people shouldn't own a Tesla out of warranty. There is no perfect decision for all owners/buyers but having more information will help you make the right decisions for you.
If you see any errors or omissions with any of the data or presentation here or if something isn't clear, please feel free to drop me a note at brian@evinventions.com and I will do my best to update or correct. If I borrowed information or an image from someone and didn't cite the source, I apologize. Please contact me and I will make the necessary updates. If you have experience and knowledge in some of the areas in this guide where I basically say, 'I don't know much about this', and would like to author a section, please reach out and we can discuss.
This page focuses on the High Voltage Battery Packs found in the Tesla Model S and Model X from 2012 through 2020. Most of the photos and specific details contained here show Version 1 packs made from 2012-2015 although a lot of basic information is similar on the Version 2 packs from late 2015-2020. While some of this information might be useful to someone working on a 2021 or newer S/X, Model 3/Y or even a Cybertruck, those all take different packs with different connections, architecture, specs, etc. If you found this searching because your Tesla simply stopped working, be aware there are dozens of failures that can happen to the vehicle's HV system that are external to the battery but still cause the car to stop moving, not charge and stop supporting the 12V battery allowing it to die. Many of those are easier and less expensive to fix, but diagnosing them and fixing them is beyond the scope of this tutorial.
The voltage in a Tesla High Voltage battery pack is plenty to kill you. Electricity is invisible. It makes no sound and and doesn't have an odor. You don't feel heat like an exhaust manifold and you don't see danger rotating like a fan belt. Understanding and having an applied knowledge of how the HV bus runs is a fundamental prerequisite to even considering working on one of these battery packs. It isn't immediately intuitive and no, removing the fuse doesn't suddenly make the pack 'safe'. With the fuse removed, most packs still have 350 Volts of potential energy ready to kill you if you touch the wrong thing. This isn't a shock that hurts like touching the side of the lamp plug wrong as you plug it in. This is a shock that stops your heart. PLEASE don't cut corners on this. Some good resources:
Hybrid/Electric training - by DiagnoseDan YouTube Videos
Hybrid and Electric Vehicle Personal Protective Equipment (PPE) and Tools - by Professor John Kelly at Weber Auto on YouTube
Loss of Isolation Diagnostics - by Professor John Kelly at Weber Auto on YouTube
Insulation Testing on Hybrid Vehicles - by Garage Gurus on YouTube
The final report from the famous "Battelle Study" ordered by NTSHA (especially check the figures in chapter 5)
Research on Electric Shock Prevention and First Aid for Electric Vehicles - paper @ Researchgate
Getting the HV battery out of one of these Teslas in a home garage with basic tools is very easy. Getting the HV pack back in takes a little more care and skill but still very do-able for most DIYers. That said, the various capacity packs weigh around 1,000 pounds, not to mention the 2+ ton car that is up on ramps and jackstands. There are a lot of things to go wrong if you don't know what you are doing or there is an unexpected failure of a ramp, jack or stand.
Getting the pack open safely and without damaging the lid is much more difficult. The lid must be removed without damaging it because new replacement lids are simply not available. Besides the practical challenges, opening the lid is also where the very real High Voltage (HV) danger begins.
You also need to consider the 'point of no return' nature of EV repairs. If you drop the engine and transmission out of your Toyota and can't figure out how to fix it or get it back in, there are many shops that can take over and you are only a Craigslist ad away from having someone take the whole mess off your hands and give you a couple of bucks for the parts. What are you going to do if you get the battery out of your Tesla, mangle the lid trying to remove it only to realize you can't fix the problem inside anyway? You can't just haul a disassembled battery pack away for scrap metal and very few people are going to be willing to take it off your hands even for free. Tesla will still be happy to sell you a used battery for $16,000, but once you take the old battery apart, they won't touch it and your $16,000 bill just became $26,000 with no valid core for them to refurbish. Don't bite off more than you can chew.