A P0171 code indicates that the fuel trim system is too lean in bank 1, meaning that there is either too much oxygen or too little fuel in the exhaust. The most common cause of this code is unmetered air entering the combustion system, which can happen due to a variety of reasons:

• Faulty or dirty mass airflow sensors
• Weak fuel pumps
• Jammed or unclean fuel filters or fuel injectors
• Defective oxygen sensors
• Vacuum leaks downstream from the MAF sensor
• Dirty or defective MAF sensors

If you are experiencing a P0171 code, you may notice a lack of power and stalling, especially when idling. To diagnose and fix the issue, it is recommended to take your vehicle to a qualified technician to repair any issues with the fuel system. However, there are some DIY methods that you can try to solve the problem, such as cleaning or replacing the MAF sensor or checking for vacuum leaks.