Q: Check engine light

My check engine light came on and I got the codes read. I don't know/remember the exact codes but it was something about the transmission not working properly and I was told I might need a new transmission. They turned the check engine light off and said if it came back on we would go from there but I've driven it pretty rigorously the past few days and it feels fine with no light coming on. But at the top of the vehicle with the temperature and all it says "service vehicle" it has said that since I've gotten the vehicle. I've also gotten the abs light on and off once the past month. And very rarely when I turn on (without moving) my vehicle it shakes/vibrates. Could this be a false code? Should I wait for the light to come back on? Should I check anything else on my vehicle? Is there any other information you could give me about this to prevent anything from going wrong?

My car has 170000 miles.
My car has an automatic transmission.