Here in the N.E. and the other night my wife called from the side of the road with a flat on her 2010 XC-60. It had gone flat very suddenly and she was lucky to get it pulled into a parking lot before doing any damage to the rim and tire. The friendly triple A guy pointed to the valve stem wobbling in the rim. There was no retaining nut. furhter inspection revealed another stem retaining nut split down the middle. My local tire store found a supplier of replacement stems with new nuts and seals. I replaced all four. The pressure sensors are ok. Bottom line, the aluminum nuts and sterms were eaten by the road grime and winter salt to the point of losing one nut and splitting another..in only 5 years. The shop recommends replacing the stems ($10 per wheel) with every tire change. Good advice.

 

Some vehicles are equipped with tire pressure monitoring system (TPMS). The TPMS could be part of the valve stem and could be more expensive to replace.
But that's a good advice anyways, everyone should pay attention to stems from time to time