Maybe it's the fact that my wagon sits outside and is subjected to the kinds of temperature inversions of a Michigan winter, but today my check engine light came on. If it was a Toyota, I'd just go buy a new O2 sensor and replace it. I drove to Ohio last weekend, and it was great. I have oil, water, and the usual fluids (salted to taste), and I noticed in a recent post that there is a way to read the codes to diagnose the exact problem. Can I do this myself?

I should point out that my instrument cluster is also misbehaving. It no longer lights up, and the speedometer works but the odometer does not. A friend of mine recently tried to install a tachometer for me, and ever since he pulled the cluster and replaced it, it's been like this.

I have a Bentley manual, but thought I'd ask here first.