Flat tire sensor

Hey guys. Yesterday, I got an error on my dash that says flat tire. I've checked all the tires and they are fine, besides the fact, they are aftermarket 20" tires. They are not connected to the ftm anyway. Is this a sensor that needs to be replaced and if so, where is it located, or can I just reset the error in the idrive?

Just a quick update, I went into the I drive and clicked on set tire pressure under the FTM panel anyway, and it cleared out any error messages of flat tires. I don't really understand but I am no longer getting an error.

You hit something pretty rough and slowed one wheel down a bit more than the other.
Happened to me before especially with low profile exaggerated rims and tires. The sensor
is on the axle and its a flat tire monitor not tire pressure monitor. So when a wheel on one
axle goes flat, it spins slower than the other wheel on that same axle. The car senses this
and triggers the fault. Not a bad design, but can be annoying because it would just tell
you have a flat and not which tire it is. It's worse with the stock run flats as you would need
a hand held pressure gauge to check every tire as run flats look inflated all the time.

Good luck.

Thank you makes perfect sense. I reset the ftm in the idrive and it seems to have cleared it out. Thanks again.