Why does preconditioning finish way before set time?

Yes it’s one of those weird things I’ve noticed. That’s why my schedules are always set for 15 minutes AFTER the actual time I want. Same for charging.

Preconditioning says "the car will be warmed up by xx:yy". Is it warmed up by xx:yy?! Yes it is. It doesn't use much energy to keep warmed up for a few extra minutes - much better this way, especially when plugged in, than when you get into the cold car because it didn't start early enough.

I’ve had two M3. They both finished heating the car early. I suspect since they heat the battery as well as the cabin, that the battery takes longer, and it reports car at temp when the cabin temp is as required. Level 2 charging timing for my 2020 was always as predicted. My 2025 takes much less time than predicted. I have no idea why.

I've noticed that. 8am precondition time and it's always ready at 7:40-7:45am every day.

It’s says it will be warmed up BY that time, not AT that time. Preconditioning also warms the battery sometimes, which takes longer. If, when you look at the app after you get the “cabin at temperature” message and you see the wavy bacon symbol, it is still preconditioning the battery BY your set time.

couldn't they heat the battery a little before blowing air into the cabin? that way it feels more like "the car is ready AT set time" instead of "BY set time"?

Battery usually requires more time then the cabin when heating

So they could heat the battery first and then the cabin? Do both need to be warming to have it preheat?

Yes the motor starts running much earlier to create heat in cold.

I think that's just the way it is, it would rather have a 15 minute buffer than miss being ready. At least they got rid of the problem where it would warn you each morning that "Charge schedule will not reach charge limit" after it started to charge when in fact it always reached the charge limit anyways. That one was really annoying as it would do that right after it started to charge (so for me like 2 hours before I normally wake up).

Probably because people would complain if it didn’t meet the scheduled time for some unforeseen reason. It was easier to just overachieve a little.

Oh yeah, I remember that one. Stressed me a lot the first time

Same. I'm also annoyed that it has to be in 15 minute increments. Is it really that problematic to have an exact time?

would be nice is all

Dang, that sounds insane. would def annoy me. Glad I missed that

It never says it's done preconditioning, it tells you when the cabin is at your desired temperature.

Was your first model 3 a rwd (base) model and your second newer one an LR awd higher model? The former is capped at 32 amps from the wall charger the latter could be at up to 48 amps. That will cut your charging time by a third

Same here

I’ve had a similar issue that it would start preconditioning like 2 hours before the set time. The longest it ever takes to reach the set temp is like 15 minutes. What a waste of energy.

No. Both are AWD units. It’s not about how fast it actually charges, but how accurate its prediction is. The 2020 was accurate from 7A (long story) to 40A, regardless of the weather. The 2025 - usually 32A - routinely will predict 3.5 hours and deliver between 2.5 and 3.

For me it’s always 15 min sooner.

Ahh yeah I've had that too I have noticed that the actual amps its drawing at home will vary- Maybe load and or temperature variables? I'm in a small house with a 100 amp panel and have tripped the main breaker a couple times by doing dumb stuff like running an oven and electric dryer while charging :-)

To be fair, 15 minutes is nothing energy consumption-wise. (I frequently hang out in my car watching Netflix for hours with the AC on… Let’s just say it takes a while to have any effect) I’d much rather it start a bit early and definitely be ready, than start at the last minute and still have the cabin be too hot/cold

You must have a level 2 charger at least cause preconditioning takes % off my battery

2 hours before is actually crazy

No, I don’t have home charging… I supercharge exclusively. Maybe preconditioning the battery from scratch takes some percent off, but I’m only talking about the extra 15 minutes. Keeping the car ready for 15 minutes won’t do anything

Because cabin reached temp before the battery, it’s not finished yet

Big house. 3 HVAC units, 320A/400A service. I don’t think it even notices when the car is charging. Nothing’s ever overloaded.

So what I have actually found is the app tells you preconditioning is done. But it really isn't. Almost always the car interior is still 5-10 minutes away from reaching the desired temps. So I always give it 10 more minutes to actually be done. It is also a known issue that many EVs lie about cabin temps. And I think this is that issue presenting itself in other ways.

It’s to compensate for extreme temps when it might take longer to reach set temp

That could be it, but no matter how cold it’s been (lowest like 10°F) it’s always finished 15 min early, even if the battery still has to warm I guess