System Too Lean (Bank 1)

P0171  means that an oxygen sensor in bank 1 has detected a lean condition (too much oxygen in the exhaust).

On vehicles equipped with two blocks (V6 V8 V10), bank 1 is the side of the engine that has cylinder #1. The P0171 is a one of the most common fault codes that triggers the check engine light. 

Symptoms

• Check engine light is on
• Lack of power or acceleration
• Engine running right
• Misfire in one or more cylinders
• Rough idle
• Poor fuel economy

Most Common Causes

• Faulty oxygen sensor
• Dirty or faulty mass airflow sensor
• Vacuum leaks
• Weak fuel pump
• Clogged or dirty fuel injectors
• Clogged fuel filter
• Exhaust leak
• Faulty air-fuel ratio sensor