P0171 code: engine running lean

Diagnostic trouble code P0171 indicates that the engine is operating with an air-fuel mixture that is too lean.

Symptoms of P0171

• Check Engine light on
• Loss of engine power
• Irregular fuel consumption
• Rough idle
• Engine stalling at idle

Common causes

• Dirty or faulty MAF sensor
• Vacuum leaks in the intake system
• Restricted fuel filter
• Weak fuel pump
• Dirty fuel injectors

How to diagnose P0171

Proper diagnosis is easier with an OBD-II scanner that can display live engine data.

View the complete technical page for P0171

Is it dangerous to drive with P0171?

In many cases the vehicle may continue to run, but prolonged operation with a lean mixture can contribute to engine or exhaust-system damage.