Nissan Repair: 2001 Inifiniti <SES> problems, mass airflow sensor, vacuum leak

Question
My SES light has been on for over 6 months. After taking it to AutoZone, they came up with the following (3) codes and possible causes of which I have no idea how to go about in solving. My main question is how MAJOR is this?

1) BBH02S12 Slow Response
- Fuel system malfunction
- Ignition system fault
- Large vacuum leak
- Faulty H02S
2) BBH02S12 circuit high voltage
- Rich A/F ration-fuel system faulty
- Blocked exhaust
- Short circuit condition
3) BBAir fuel ratio (AF) sensor 1 circuit slow response - BBbank 2
- Lean A/F ration - fuel system faulty
- Large vacuum leak on engine
- Faulty MAF sensor
- Faulty AF sensor

Answer
Rebekah,

The first code is probably the gas cap being loose or even a loose hose clamp on one of the fuel or vapor lines.  This is not major other than the labor to track down the leak.  The third code is related.  But, it could be the mass airflow sensor.  That is a plug and play device that you could change.  The second could be the throttle position switch as these are known to fail.  Probably $100 bucks for the part on the TPS and another $200 bucks for the mass airflow sensor.  Neither of these are difficult to install.  I would get a Haynes Manual for instructions on how to check them prior to just replacing them.  After you are done the parts store can reset the code or you could just disconnect the battery for five minutes to clear the code yourself.  Also, for $65 bucks at Harbor Freight you can purchase your own code reader that will work with any 1996 or newer car.