Yesterday the check engine light came on and I am getting an error 43 code. I was on the highway doing about 55 mph, I'm usually just around town so no really fast driving. Could a bad catalytic converter cause it? It is rattling quite a bit. With the code on the jeep was still running as usually, no rough idle or anything. Two other things I've done are when the check engine light came on I was just coming back from having the oil changed. I usually do it myself but didn't want to lay out in the snow. The other thing was I let my wife use and the gas was down to 1/4 full and she use the 91 octane gas. I'm not sure that either of those could have anything to do with it. Thanks for you help and input!