Today I put winter tires on my 2011 328 e90. I bought the tires in 2007 and previously used them on 2007 e92 335. I expected to have the tire pressure light to be on - I read on the forum that 2007 TMPS are different from the 2011 ones. The light is not on and no warnings displayed. How can i tell if the system is working besides deflating one of the tires? Thank you.