Pull the dipstick and check the oil for color and smell
a clear red/brown color and a clean"oily" smell is normal. check a bottle of new ATF for reference.
If it is a dark dirty brown color and/or bitter/pungent smell, it likely needs some work.
Codes are set when electronic sensors and controls detect problems in the operating system. These codes are stored in the computer and read with another computer that the shop attaches to the vehicle. The codes refer to the failure of specific components or circuits and are a place to start the diagnosis.
JD