Ok, I have a 2004 Hyundai Elantra that I bought used 8 months ago. It has just over 72,000 miles on it and the check engine light came on. I took it to Checker's and they gave me the P0420 Catalyst System Efficiency Below Threshold (Bank 1) code. I asked for the english version and he said O2 sensor or Cat and reset the code. It came back on tonight while I was at work (delivering pizzas) and one of the other drivers suggested to tighten my gas cap. It turned it off!! So was that the problem the whole time or was I just lucky this time? Also, if it is the O2 sensor or cat will my continued driving totally destroy my car? And is there any way to find out which it is or do I just have to suck it up and pay Hyundai $100 for a diagnosis?
Any help would be really appreciated because I am really afraid that if I continue to work that my car is going to blow up or something but if I don't work I won't have the money to fix it. HELP!!!!!