 I bought a 2007 Altima 2.5S 4-cyl from a private seller in July 2011. It had 117,000 miles on it, mostly highway. The car was in great condition and I even had it inspected at a shop before buying it. About five days after driving it, the check engine light came on. I thought there couldn't possibly be something wrong with it already, so I manually turned the light off and waited...two weeks later, it was on again. The catalytic converter was the problem and I had it cleaned out, but was told that it still may need to be replaced. Everything was fine for about 3 months, but the CE light just came on again at 121,000 miles. I don't want the engine to get ruined, so I'll have to fix it asap. 