i have a bmw 328 i that failed smog inspection and they gave the results of the fault code which is p0430-p0420 (cat efficienecy threshold bank 1&2) if anybody can tell me what those codes mean i'd appreciate it thanks.

If you have the original converter on it it may be constricted causing the exhaust gases to back up. Bank 1 is pre converter and bank 2 is post. If you have over 80,000 miles and the oxygen sensors have never been changed that is a good place to start.

bank means 02 sen volts to low or to high bank 1 befor the cats bank 2after the cats your car is running to rich exhaust could be a vaccum leak intake or vaccum line. check all.