Maybe it's the Michigan winter, but I've got a check engine light on. I saw a recent post that says it might be the O2 sensor. Is it easily accessible? There was also some talk of checking codes. Can I do that myself?

I drove to Ohio last weekend, and it ran great. I have oil and water, so that's not the problem. It's not making rattling noises like it's not getting oil.

The instrument cluster also does not light up and the odometer doesn't work. The speedometer works fine. The cluster was removed and replaced when a friend offered to install a tachometer.

Is any of this expensive? I replaced the alternator last winter in my driveway, so I've at least some mechanical ability.