Toyota Corolla Code P0171 Check Engine light

Code P0171 on Toyota Corolla Q: What could cause the code P0171 on 2002 Toyota Corolla? A: The code P0171 reads "System Too Lean (Bank 1)". This means that the air-fuel mixture coming in to the engine is too lean, or there is too much air and too little fuel. This could be caused by a number of reasons, such as bad airflow sensor, vacuum leaks, low fuel pressure, clogged fuel injectors, etc. To know exactly what caused the problem, your mechanic can do a few tests.
From my experience, the airflow sensor problems are fairly common; sometimes the sensor just gets dirty and gives false air flow readings causing lean condition. Again, your mechanic can test it.
If the airflow sensor is causing the lean condition, it will need to be replaced. If the sensor is just dirty, your mechanic may suggest to clean it (cleaning the airflow sensor is very delicate procedure) as a temporary solution - sometimes this could work.