http://www.allpar.com/fix/codes/faults/code-51-52.html

Basically, running rich, which your smog test agrees with. Not likely the O2 sensor here. Run thru the driveability troubleshooting guide on the link. Might be something like coolant temp sensor stuck cold or similar.


They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.