I recently got a 2006 chrysler sebring convertible GTC which has 72K miles
After driving it for 200 miles, check engine light came up and also acceleration became slow and transmission started to vibrate
I took it to Autozoe and got the code P0430
Then I went to the Mechanic, he checked and reset the code and asked me to come again in case the engine light comes on.

And problem disappeared (transmission was smooth and acceleration was great). After 30 miles, the car steering became hard and it stopped running, the check engine light came again. I started the car again but transmission is now vibrating again and acceleration hesitates and is slow

What should I be doing? Should I go to the Chrysler dealer to get to know the problem? Is this going to be expensive fix ?

 

Try taking it somewhere where they have better code reader. There may be something going on that the code reader at the parts store can't get to. Things like transmission codes require a more sophisticated code reader although there is usually an indication that more codes are available. No way can anybody here give you a full diagnosis.

"After 30 miles, the car steering became hard and it stopped running..." What happened there was that the engine stalled first and then, because of that, the steering became hard. The engine must be running for the power steering to work.

With a used car you probably don't have any history of maintenance for the car. At 72,000 miles it's probably due or overdue for some preventative maintenance like transmission fluid change, etc. The owners manual will spell out needed service. If you don't have one, download it from chrysler.com

 

Thanks
Where would I get better code reader apart from dealer?

 

A good reputable garage should have a good quality code reader. If you are convinced that it's a transmission problem (you never said what caused you to arrive at that conclusion) then a place that specializes in transmissions would be a logical place to go. These high quality code readers are expensive, like $15,000, which is why Joe-down-the-street doesn't have one. As a result, most places that have made the investment are going to charge you a diagnosis fee for hooking it up, unlike the parts store which doesn't charge you but may not find out what is going on.
Ask around town, friends and relations to find a good place to take the car if you don't want to go to the dealer. Dealerships are often, but not always the most expensive option. For something like a transmission, the dealership may often subcontract the job out to a transmission shop. Personally, I'd rather deal with a guy who does the same thing all day every day (like a transmission shop) rather than a dealer who may fix a transmission a few times a year. My experience with dealerships is that they would much rather "remove and replace" almost anything rather than get inside a component and repair it.

 

I took the car to the mechanic, he said he fixed it and I didn't see the code anymore but car still vibrates
He changed the camshift sensor
Need to figure out where to take the car to

 

There are many possible causes for vibrations. Anything that rotates can cause a vibration. Could be the engine, could be the transmission, could be driveshafts, brake rotors, tires, air conditioning compressor, suspension. Convertibles, by their nature, tend to have more body shake than sedans.

You need to be a lot more specific about your vibration. When does it occur? Moving or stopped, slow or fast, certain speeds or all speeds, braking or accelerating, smooth roads or rough. Where in the car do you feel it? Seat? Steering wheel? Brake pedal? The more specific you can be, the more likely it is that somebody can help figure out what is causing the problem.