Oh man, just replaced the transmission in my van a couple months ago.... And yesterday that darn Service Engine Soon light came on.
OK, took it in because the oil needed to be changed anyway. I figured some sensor had gone as we've got 109K on our 1999 Dodge van. Well, yes indeed. The CO2 sensor went out... $233 for the repair.
I think that it's time for one of those new snazzy hybrid deals that gets a gazzillion miles per gallon.