i have a mk4 golf and my check engine lite is on and i failed emissions the dude said my catalyst system is below threshold bank1 he didnt tell me what it means tryin to help me out  

For us to help you, we'll need a lot more information than that! Are you driving a VR6/R32/1.8?? Do you have the code number being thrown with that check engine light? There are several questions unanswered here that we'll have to know before we can give you any help!  

from my experience as a vw tech i would say the most likley cause of this fault is the cat. converter. contact your local dealer. there is a federal mandated law on that covers cats. for eight year eighty thousand miles.  

its a 2.0 8v ive already have 90,000 miles on it but the sheet said that my cat already passed my obd diagnostic was what failed and i dont have the code number sorry if none of that is helpful