System too lean?

I have a 2002 Celica and lately my check engine light has come on. I took it to Autozone to get checked. The code came out to be P0171. Which means System Too Lean (Bank 1). I have no idea what this means what so ever. Can anyone help me out or think they know what this could me?

Check the following:
Air induction system
Injector blockage
MAF meter
Engine coolant temperature sensor
Fuel pressure and flow
Exhaust leak
Open or short in A/F sensor circuit
A/F ratio sensor

po171 system too lean is caused by a faulty oxygen sensor, Bank 1 means that it is the first one closest to the motor on a four cyl. usually if something else it will come up with more than one code at the same time

Don't limit yourself to the A/F ratio sensor. Any of the systems I listed could cause that code.

Like he said, I had this same problem occur after a cold-air intake install.

The guy took it to a local repair shop that was doubling for parts changers and simply charged him $143 for an O2 sensor that he didn't need and used a Bosch Universal which made matters worse.

Do the research and you can save yourself some serious headaches later.