Sylvie Goes Back to the Shop — Round 2

Short version: Sylvie’s battery died at 78,000 miles two weeks ago — replaced under warranty for $0. Last Monday, she drove beautifully with FSD v14.3 Lite on a 2018 Model S 100D. I thought we were done. Then Tuesday, completely unresponsive. Flatbed again. Round two. At least the tow was covered.

The battery replacement

Two weeks ago, Sylvie’s battery finally gave out at 78,000 miles. That’s not terrible for a 2018 Model S 100D — the early 100 kWh packs had a known failure mode around that mileage, and the warranty covers it. Tesla replaced the battery under warranty, zero out of pocket. I was relieved.

The new pack felt great. Range was back. Charging behavior was normal. I figured I’d gotten lucky — the battery died at the right time, in warranty, with no drama.

FSD v14.3 Lite — the good day

Last Monday was the best day Sylvie’s had in months. The FSD v14.3 Lite update had just landed on this 2018 Model S 100D (I covered that in the last video), and it worked. Really well. Smooth intersection handling, better unprotected turns, the whole v14 driving policy on legacy HW3 hardware.

I drove around for an hour, documented it, genuinely thought “we’re back.” The car felt new again. The battery replacement plus the FSD update felt like a second life for an eight-year-old vehicle. I parked her Monday night feeling good about where things stood.

Then Tuesday

Tuesday morning, Sylvie was completely unresponsive. No screen wake. No notification. No response from the key fob, the app, or the charger. Dead. Not a gradual decline — a hard stop.

The timing could not have been worse. New battery, new software, and then nothing. The immediate suspicion is that the two events are related — new battery install and new FSD firmware hitting the same vehicle in the same week — but correlation isn’t causation. Could be a coincidental electrical fault. Could be the BMS having an opinion about the new pack. Could be bad luck.

Either way, the result was the same: Sylvie needed another ride on the flatbed.

Round two

The tow truck showed up, loaded Sylvie up, and headed back to the same shop that did the battery replacement two weeks ago. At least the tow was covered — warranty service includes towing, and they didn’t push back.

Round two. I’m not frustrated so much as I am curious. A 2018 Model S 100D is a complex machine with a lot of interdependent systems, and swapping a battery on an eight-year-old vehicle can expose other weak links in the chain. If that’s what happened, it’s not great, but it’s understandable.

What I expect from here

The shop will diagnose. If it’s a BMS communication issue with the new pack, that’s a straightforward fix. If it’s something else — a controller board that got bumped during the swap, a ground fault, a power distribution issue — it could take longer. I’ll follow up when I know more.

The good news: Sylvie is under warranty for this stuff. The bad news: being without the car for another stretch.

Bottom line: Sylvie’s back on the flatbed. Battery replaced two weeks ago under warranty, FSD v14.3 Lite working beautifully on Monday, completely unresponsive by Tuesday. Round two at the shop. The tow was covered, and I’ll report back when we know what went wrong. Subscribe if your car has been to the shop more times than you have this year — you’re in good company.