2021 Tesla Model S — fast charging tapers earlier than it used to — trying to narrow this down

Intermittent stuff lies if you only catch it once. Get a real battery/charging test on the 2021 Tesla Model S, not just resting voltage, before blaming a module. You'll know quickly if you're on the wrong tree. On “fast charging tapers earlier than it used,” that was the fork that mattered for me. This is from a 2021 Tesla Model S in Miami. If you share a photo of the worksheet, easier to sanity-check. Not interested in a five-hour wait for a shrug.

This is usually cheaper to test than to guess. Swap the cheap/easy piece first on the 2021 Tesla Model S and see if the fault moves. Save the big job until that test fails. Do that first. That's my plan before I call anyone.

Start with the test that can prove you wrong. Move a coil or plug on the 2021 Tesla Model S if it's cylinder-specific and see whether the code follows. That's the branch I'd chase this week. Had a similar mess a couple years ago and that's what finally sorted it. I'd rather pay for diagnosis than a second guess-repair.