If you have an AutoZone nearby, they will hook up their meter for free and tell you what codes are coming up and what they mean. If it's a real issue you can have it addressed -- if it's relatively meaningless, they can clear the code for you and make the light go off.

Regarding the wheel shake -- he didn't go through any mud or anything did he? If you get some mud inside a rim, it what shake like crazy.

Don't ask how I know -- long story.