Cadillac STS Forum - 2005 through 2012 Discussion, Yay! PO174 fixed in Past Cadillac Vehicle Discussion; Turns out, when I changed the air filter weekend before last, I didn't get the hose clamp on the intake ...
Turns out, when I changed the air filter weekend before last, I didn't get the hose clamp on the intake hose connected to the intake manifold quite tight enough.
Tip: use an 8mm or 5/16" nutdriver or socket to tighten it, not a flathead screwdriver.
Edit: Well, it stayed off until I stopped for about 10 minutes on the way home, then the CEL returned. I put my code reader on it a short time after that, when I arrived home, and whadda know...no codes.
I'm carrying the reader in the console for the time being. If nothing else, as a threat to the engine computer.