Dealer replaced O2 sensor under warranty in Dec. Also had crank position sensor recall done. Since then and 4 tanks of gas later, mileage has dropped from ave. of 23 before to about 19. Performance seems OK. Lots of air in tires. Parking brake off, etc.

Do either of these parts that were replaced require some sort of calibration or setup that the dealer could mess up and cause a drop in mileage? or are they just plug and play?