What is a P0171 on Mazda protegé 1999?

P0171 is an OBDII code that indicates that the engine's air-fuel ratio is lean, meaning it's not getting enough fuel. There are a number of potential causes for this, including:

- A faulty oxygen sensor

- A vacuum leak

- A dirty fuel injector

- A faulty fuel pressure regulator

- A malfunctioning catalytic converter

To diagnose the cause of the P0171 code, you'll need to connect an OBDII scanner to the vehicle and check the live data. This will allow you to see the air-fuel ratio and other relevant data, such as the oxygen sensor readings and fuel injector duty cycle. You can then use this information to narrow down the possible causes and make repairs as necessary.