Chrysler

My car didn't want to start very well in the very cold weather,, the other day it was 18 out,, the car started but the check engine light came on,, took it to the dealer and they said the Powertrain control module was bad,, they replaced it and told me to pick it up,, they drove it in for me,,then the check engine light came back on,, now they said the 02 sensor was bad,, the car only has 5000 miles on it,,, What is wrong with my car??