REX Wont Turn On

My CEL light came on when I started my trip but now I am on my way back home from a Denver to Moab trip and the Rex wont turn on. I just filled with gas and came off of the charger in Frisco where I got an 80% charge. The REX worked perfectly for the whole trip, I have been using it to hold charge once below 75%. I see a few posts about overfilling with gas and the gas sensor is causing the problems. Any thoughts?

In case you're not aware, the REx engine won't start if the battery pack's charge level exceeds 75%, so you'd need to drive until the charge level drops below 75% to determine whether there's something wrong with the REx system.

Unfortunately, the CEL illuminates for all sorts of reasons, so it's not possible to determine why it's on without connecting a DTC (Diagnostic Trouble Code) reader familiar with BMW DTC's to the diagnostic port.

Overfilling the gasoline tank would likely not prevent the REx engine from starting but might set a DTC.

A bad fuel tank pressure sensor wouldn't prevent the REx engine from starting but could prevent opening the fuel door.

It's possible to force the REx engine to start while an i3 isn't driving. This is used for emissions testing. Having a BEV, I don't know what the procedure is. However, a REx owner will likely post the procedure. You could use it to test whether the REx engine will start. If it won't, all sorts of problems could be to blame.

Fortunately, after you ascend to Vail Pass, it's mostly downhill all the way to Moab. However, finding public charging stations is probably difficult.

Good luck!

Some of the sensors don't like to see actual gasoline on them at all...always stop filling the tank when it shuts off...don't try to add a little bit more.

Note, if it's super hot and the tank is deep, there is also expansion as the fuel warms up, so being careful about how full it is can be part of the problem. Make sure the gas cap is tight.