The Malfunction indicator light went on, and won't go off. on 2005 Dodge Grand Caravan

The Malfunction indicator light went on and I've had it looked at by a mechanic twice. Says he checked on diagnostic machine, and not to worry. When I start it, it runs a little shaky, but then ok when I drive. Should I have it checked out, don't want major engine, transmission, or emission control system damage. The light stays on, it doesn't flash.

Asked by for the 2005 Dodge Grand Caravan
What codes do you have?
Well when I turned off and on the ignition 3 times, (what I read I have to do to get the code), it just read "done" which I was confused. I didn't get any P codes like I've been reading from others. The mechanic didn't tell me what codes he saw. I guess I could ask, but did I do it right by turning off and on the ignition 3 times? The odometer read "done". I tried it again and again, but then it didn't give me anything, just the mileage remained. Appreciate your help!

I did the same thing this morning to get the codes, and I got P0302 and then P0304. After reading about it, I guess the last number of the code tells me what cylinder is causing the problem, yes/no?

Thanks for your help!