Service Engine Soon P0171 and P0172

[fin240sx]

I went to Autozone Friday night and borrowed their scanner to read the code. The scanner read these codes.

P0171 Fuel System Lean, Bank 1

P0172 Fuel System Rich, Bank 1

The car is 2000 G20. I have no idea what these code meant. The sales person recommend me buying the Oxygen sensor for the Front. I bought it and installed it last night (Tuesday). The "Service Engine Soon" dissappeared. The next day it came back on. Is it the oxygen sensor or something else? Thanks in advance.

[fin240sx]

I'm sure somebody have experienced with this problem before. Please help.

[Raxephon]

2000 Infiniti G20 Factory Service Manual http://phatg20.net/modules.php...d=180

Start at EC-273 and go through the steps.