Check engine Codes:need help

[kurkovn2005]

I have a 2002 audi a4 and I need to get the check engine light off, I have these codes can someone help me to find out what in the world I need to change or do I just guess. It is

P0420: BBCatalyst system efficiency below threshold bank 1

P0171: BBSystem too lean-bank 1

then there is other ones like a faulty cylinder

If anyone knows what to fix for this specific car please let me know, it will be helpful.

[vectortech]

P0171 is almost always a vacuum leak in the intake- or possibly a messed up o2 sensor. These both need tested.
The other one is pretty well cut and dried that you need a new cat. converter. Not too many ways to get around this one.

Please post all of them- also let us know how it is running.

[kurkovn2005]

Thanks man,
It was for my freind. Ya he got rid of it cause it had too many problems with the electronics. But still thank you.