I thought you bought the sensor from the dealer? The tire "might" have had a bad seal at the rim.. backside since you did check the outside and valve stem.. 65 PSI could have been enough to force the seal at the rim.. not saying it's your case.. but when my rear tires were mounted.. they were balancing them and from the shop window I noticed one wasn't running true.. he put the weights on and all and started rolling towards the car with it.. then stopped and had noticed the bead had not seated fully at the rim.

Edit: And unless i'm mistaken in what I've read elsewhere.. a strong magnet is actually use to activate a new senor to life.. but then as noted it has to be registered to the cars computer.