ah, that clear things up. thanks again.
Again, out of curiosity, anyone knows what is the point of the pre-cat testing while there is another main cat after that(other than extracting more money from us) ?
BTW, I saw some local mechanics offer fuel system flush service, would that be equivalent to the B12 treatment ?
Oh, I forgot to mention, the O2 sensors have been changed may be 2 times(the last change is about a year ago or so, forgot which one at the moment though) and I don't get other DTC code so I would assume they are still good. But may be it is good idea if I have to change the pre-cat anyway(and assume they don't charge me extra labour for the O2 as they have to go to the same area).
