How to tell AI3 vs AI4, heat pump and LFP vs nickel from a Model 3 or Model Y VIN

A used Model 3 or Model Y listing gives you the year, the trim and the kilometres. It rarely says which self-driving computer the car has, whether it has a heat pump, or which battery chemistry it uses, and all three change how the car charges and gets through a Canadian winter. Some of that is written in the VIN, some can only be narrowed down from it, and some you have to check at the car. Here's which is which.

What the VIN actually says

A Tesla VIN has 17 characters. The ones that matter here:

No character says “AI3”, “AI4” or “heat pump”. Those are worked out from the model, model year, factory and drive unit, against the documented dates when the hardware changed. Outside a changeover that's reliable. Inside one, it isn't.

The VIN has a model year, not a build date

A model year usually covers cars built from about October of the year before through December of that year, so the VIN alone can't place a car on one side of a mid-year change. For that, read the manufacture date (month and year) on the label in the driver's door frame. Near a changeover, that month is what decides it.

AI3 (HW3) vs AI4 (HW4)

• Model 3: model year 2024 and later (the redesigned car) have AI4. Earlier Model 3s have AI3, except the oldest: US-built cars moved from the older HW2.5 computer to HW3 around March to April 2019, and some Shanghai-built cars from late 2019 to mid 2020 shipped with HW2.5.
• Model Y: model year 2022 and earlier have AI3. After that it depends on the factory and build month. Fremont and Austin mixed the two computers from about late May 2023 to January 2024. Berlin changed over around December 2023 to February 2024. Tesla said Shanghai-built Model Ys had AI4 from February 2024.

Check the carInside one of those windows, the VIN can't decide it. On the car's screen, go to Controls > Software > Additional Vehicle Information and read the computer listed there.

Heat pump

• Model Y: every one has a heat pump.
• Model 3: the heat pump arrived with the October 2020 refresh. Model year 2021 and later have it. Model years 2017 to 2020 use a resistive heater, which costs noticeably more range in the cold.

For a Model 3, character 10 settles it: M or later means a heat pump, L or earlier means a resistive heater.

LFP vs nickel battery

• Dual-motor Model 3s (Long Range, Performance) use nickel-based packs throughout.
• Single-motor Model 3s switched to LFP partway through: Shanghai-built cars around October 2020, North American-built cars around November 2021 to February 2022.
• Model Y: Long Range and Performance cars use nickel-based packs. Shanghai-built single-motor Model Ys are generally LFP (community-documented). For other single-motor Model Ys, confirm it on the car.

Check the carIf character 7 is F, it's LFP. Otherwise, open the charge screen: if it recommends a daily limit of 100%, it's LFP. Nickel packs recommend 80 to 90%.

Why it matters: LFP is happy charged to 100% every day, but loses more displayed range in deep cold and charges slower when frozen. Nickel handles cold better but prefers an 80 to 90% daily limit. Neither is better overall.

What a VIN can't tell you

• Battery health. The VIN shows how the car was built, not how much capacity its pack has left. Ask for a battery health test, or have it checked in a pre-purchase inspection.
• Condition and history. Accidents, flood damage and past owners come from a vehicle history report and an inspection, not the VIN's characters.
• Open recalls. Look the VIN up in the official recall database (Transport Canada in Canada, NHTSA in the US).
• Paid software. Features bought as software, like Full Self-Driving, depend on the car's account, not its VIN. Confirm them on the car's screen and with the seller.

Build windows come from published reporting and community documentation of Model 3 and Model Y production. Dates are approximate, and cars built near a change can go either way. Always confirm on the car.