It will distinguish once tire warms up, however your pressures are WAY too low to drive if it is on. With low pro tires you really can't see the 5lb difference. I set my tires at 40 and let them cold soak over night. In the morning I set mine to 31.5 front and 30.5 rear. Getting pretty even tire wear on my car.
http://www.sears.com/craftsman-progr...p-02823020000P