Hi , im new here and just purchased a 2011 ram 1500,i have been a ford fan for 20 years,my last ford f 150 gave me quite a bit of troubles after 75,000 miles . so i figured i try something else, anyways, i have had the ram for about 3 weeks now,yesterday it was about 4 degrees out, when i went to start it the check engine light came on, i checked it on a code reader .it was the o2 sensor upstream bank 2. it then went off on the way home. to day the gas mileage display reset itself ?. but i have noticed when im sitting at a light or just idling the mileage keeps fluctuating ? i dont think it did this before? does any body know if theres will keep changing while standing still? thanks for any help, i hope i haven't made a big mistake switching brands, kinda early to be having problems. thanks again greg.