A few months ago the “check engine” light came on in my Infiniti I30. I took it in and they said the catalytic converter was triggering the light, and that meant it was probably an oxygen sensor. However, they said that all the oxygen sensors seemed to be working fine when they checked, so they recommended I watch my gas mileage closely but not start replacing senors until they could figure out exactly what was going on. They said they would keep checking it when I bring it back for oil changes.
So I’ve been driving around for a few months with the “check engine” light on, and have not noticed any change in mileage.
Last week I drove to Colorado Springs, which is about 6500 feet above sea level. The first time I started the car after arriving I noticed that the check engine light was not on. I drove all over Colorado for a week and the light never came on. Then, when I was driving home, the light came on again in Kansas and has stayed on ever since. What do you think?