TPMS instability. Why

I have experienced intermittently the TPMS warning light coming on. I routinely check tire pressures and even when the light comes on there is generally less than 2 lbs difference between all the tire pressures. I do not know if the spare tire has a TPMS sensor that is causing the problem, but any ideas would be welcomed and also any information on whether this is a warranty issue (Purchased May 2014 and only 28K miles) that the dealer can fix. Ideas please

 

Not sure what year you have but I would for sure check the spare ....

 

The TPMS light comes on when it senses a drop below whatever the initial pressure was set at in the system , this can happen during cold temps

 

Depending on your year you should be able to set them all including the spare to 32 or whatever psi you want and then use the TPMS calibrate button

 

My spare has a TPMS
I just set my sensor for 28lbs run my tires at 34lbs
The manual shows how to recalibrate