waih136

My gf has an 02 tt that has the mil keep coming on once in a while. i clear it and it keeps coming back. It's the same codes over and over again and honestly i don't jack about turbos or the proper terminology, even though i've replaced far to many parts on that thing. i was just wondering if anyone has idea where to start or ways to narrow it down to save some $. There hasn't been any difference in drivability with the lights on but winters coming and i'd like to get it done before then. This is what the codes pop up as.
16804 - Catalyst System; Bank 1: Efficiency Below Threshold
P0420 - 35-10 - - - Intermittent
17608 - Boost Pressure Control Valve (N249): Mechanical Malfunction
P1200 - 35-10 - - - Intermittent
16795 - Secondary Air Injection System: Incorrect Flow Detected
P0411 - 35-10 - - - Intermittent
18010 - Power Supply Terminal 30: Voltage too Low
P1602 - 35-10 - - - Intermittent
Thanks for any help, hopefully can get this done before anything else goes wrong with it. Edit: As i'm going through some of the easier accessed stuff i beleive the waste gate is bad. very small leak when i blow through it and i hooked a 9v battery up to it and nothing. Hooked it up to another one and i could clearly hear the click. could this cause all the issues?