Yup, they're all related to the sat-nav. Speed will be the speed pulse (will probably show as OK when the car is moving) and reverse will be the reversing light switch feed (so it should show OK if you engage reverse gear.) Both are used to increase the accuracy of the positioning, and to maintain positioning when you temporarily lose GPS (e.g. in heavily built-up areas or tunnels.)
I'm not sure about the other readings, though I think mine always used to give the bus error too.
Great stuff - thanks Horatio. Having already had a poorly car on day 2 of ownership, I was dreading more bad news so thanks for putting my mind at rest.