Advice about non factory radios

Hello, I went to put my old cd player into my 2003 cavalier. I bought the wiring harness, little to find out that it suggusted using more parts. The parts were to keep the chimes when you open the door. Out of curiousity i went to go see how much it would cost ( i am saddly some what relint on the chimes). The guy said that the kit that is need to keep the chimes is a hundred bucks, and would have to be mounted in the back. I saddly don't have a hundred bucks to spend. The guy at the stero place said if i didn't have this kit, the check engine light might go on and off, and if i go to get my car service the dignositics wouldn't read correctly. Is this true? Do i have to spent the money in order to get the new radio in?

Thank you :)

There are rumors that all these problems may occur in 2000+ J-Body vehicles. I can tell you from experience that you will lose the door chimes for sure. everything else seems fine for me.

My friend took one of his head light bulbs out and the check on light came on in his 2000+ Z24. I wouldnt doubt it one bit if it was true what he said, lol.