P0171, P0172, P0174, P0175 Error Codes Reason & Explanation

 P0171 / P0174 — SYSTEM TOO LEAN 

 Common Causes of LEAN Condition 

• Cracked intake hose
• PCV valve stuck open
• Intake manifold gasket leak
• Brake booster leak
• EVAP purge valve stuck open
• Underreports airflow
• Engine adds fuel → triggers lean code
• Oiled aftermarket air filters
• Dirty air intake system
• Weak fuel pump
• Clogged fuel filter
• F