Yep, they pulled the codes. They tried everything (and I watched them do it--I didn't just take their word for it). Like I said, these guys are on the hook if the motor grenades itself, so they gave it the fine-tooth comb treatment. It came up clean. Cleaning the MAS was the last resort, and, since I had a day a week or so ago when the light mysteriously 'fixed' itself and then 'unfixed' itself, all parties concerned are convinced it's just a little short somewhere, or a false signal from the oxy sensors.
[addsig]