Originally Posted by Eric.ingram

I'm trying to understand this. I just changed tires on my 09' Tpms read normal psi numbers before Now it says +9 fronts. + 2 rears, It was -9 and negative 4, with flat tire light on. how can it be negative psi??? Then I saw a post about zeroing What do you do? Zero all 4 and drive it until the psi reads back out? I can't find the reading just the + /- numbers are showing Thanks