So you ignored the low pressure warning last year, it went off again in the spring and you didn't have any issues, right? Did you physically check the tyre pressures last year or after the light recently came on? Surely that's the obvious thing to do? It could just need a few psi adding and you should be checking them regularly for safety anyway. My GS has a second TPMS button that's intended for a second set of wheels, maybe winters. It's hidden away under the passenger dash if I recall correctly.