Why we have to reset the low tire warning (how BMW’s TPMS works)
Very nice explanation by Barry45RPM:
The way these German TPMS’s work is that when you “Reset” the system, this is the new memorized amount of air pressure that the system stores. Whatever pressure is in the tires at that moment is now considered to be the new “proper inflation pressure” comparison point. Later on if a tire pressure is no longer at that memorized pressure the system notifies you.
When you reset, the then current pressures become the standard you wish to compare to at all times.
So, if you are driving around, and 1 of your pressures is currently low at 23 lbs and you reset, you will only be notified when your tire pressure drops several pounds below 23 lbs. Thats why you should only reset when you are sure that all the tire pressures are at your desired, correct pressure.