I haven't ran across an in depth explanation of what occurred with refueling and the fuel tank with my 2020 i3, so I thought it might be helpful to share my experience to warn others.
When I took delivery of the i3, the salesman didn't give any kind of warnings about filling the REX fuel tank. And with winter approaching and no need for the REX to run due our limited travel range, I thought I'd fill the fuel tank and be done with it. So I did just that, filled the fuel tank. And not to the point where it was running out. Likewise, I didn't raise the fuel pump higher in the fuel neck to get the last drops in, etc. This was in November 2020.
Four months down the road, the REX had succesfully ran twice for maintenance. After the second maintenance phase run, the REX triggered a check engine light. When it didn't go off, we took the i3 to a dealer.
The dealer then told us the car had $1,800 in damage to the emission system from the fuel tank being overfilled. And they wanted us to pay for it, claiming it's not a warranty repair.
I did a Google search on the topic while they had the car and while waiting to see if this would get paid for. I only found one other person in a similar situation. They claimed they had a similar problem four times and each time BMW fixed the car for free. The person said the BMW dealership repeatedly accused them of overfilling the fuel tank. They denied doing so.
A search of the i3 manual doesn't shed adequate light about what occurred. For example, an i3 manual at i3guide dot com states the following: " "Do not overfill the fuel tank; otherwise fuel may eslide, causing harm to the environment and damaging the vehicle." Observe the manual doesn't warn about damage to the emissions system by merely filling the fuel tank.
Reading that excerpt, in my opinion, from the manual doesn't warn you that merely filling the fuel tank on this car can translate into an $1,800 repair bill and the REX being disabled. To me, it comes off as more of a warning about damaging the paint and the environment.
The owner's manual for my car isn't much better at BMW's website. First it reads "Fuels are toxic and aggressive. Overfilling of the fuel tank can damage the fuel system. Painted surfaces may be damaged by contact with fuel. Escaping fuel can harm the environment. There is a risk of damage to property. Avoid overfilling."
But then manual contradicts itself. First saying this: "The fuel tank is full when the filler nozzle clicks off the first time." And then saying this under emergency refueling it says: "Refuel the vehicle as usual. The excess pressure in the tank may make refueling difficult, for instance the fuel pump nozzle may shut off frequently."
So if the fuel pump nozzle is "shutting off frequently," you wouldn't be advised to stop with the first click off, would you while performing a fueling after opening the fuel tank when the button didn't work and you had to do it from inside the front trunk. Which would then potentially result in an $1800 repair to the emission system: a charcoal canister, lines and a sensor. A crazy amount of money for those items in my opinion about that too.
Likewise, setting the fuel nozzle to auto run and it not cutting off and the result of that adding to much fuel could theoretically trigger this kind of repair too.
Just wanted to warn all of you to be very careful when refueling this car. I'm almost scared to put fuel in this silly thing anymore after this incident. I'll certainly be adding far less than two gallons just to be precautionary from here forward.
After some arguing, BMW agreed to fix the car "one time" as a "goodwill" repair, but they initially insisted that we pay for the damage.
Cars should be built as dummy proof as possible in my opinion, but not the case with this i3 if you can do so much damage by merely filling the fuel tank.
This is priceless in the manual too: "With a driving range of less than 30 miles/50 km the engine may no longer have sufficient fuel. Engine functions are not ensured anymore. There is a risk of damage to property. Refuel promptly."
So you're screwed either way. Too little fuel, or too much fuel apparently cause damage.