My low tire pressure light is on and won't go off, why? on 2008 Chrysler PT Cruiser

It happened right after I hit a pot hole. I took it to my normal shop and they could not find the reason for it. They checked all of the sensors and even used a diagnostic computer to look for error messages and could not find any. When that didn't work they read the manual for the car and still no success. What should I do now?

also check your spare tire pressure