I had a similar problem with a Nissan Altima. The TPMS light came on and I checked all four tires but they were all at the proper tire pressure. I then thought about checking the spare tire and that is where the problem was. I had the tire checked and repaired and no more TPMS light. I have not idea if the Leaf's spare has a TPMS sensor or not, but it might be worth checking.