Vacuum leak (intake manifold gasket, brake booster hose). Faulty mass airflow (MAF) sensor. Weak or failing fuel pump. Clogged fuel injectors. Exhaust leak before the O2 sensor.

Which cars are affected by P0171?

P0171 is most commonly reported on BMW, Ford, Vauxhall, Toyota, Volkswagen vehicles, but can appear on any make.

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P0171

Medium severity

System Too Lean (Bank 1)

The engine control module has detected that the air-fuel mixture is too lean on bank 1 — meaning there is too much air or not enough fuel entering the combustion chamber.

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Common causes of P0171

1Vacuum leak (intake manifold gasket, brake booster hose)

2Faulty mass airflow (MAF) sensor

3Weak or failing fuel pump

+2 more causes

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Commonly affected vehicles

BMWFordVauxhallToyotaVolkswagen

P0171 can appear on any vehicle — these are the makes where it is most frequently reported.

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Related fault codes

P0300High

Random/Multiple Cylinder Misfire Detected

P0420Medium

Catalyst System Efficiency Below Threshold (Bank 1)

P0172Medium

System Too Rich (Bank 1)

P0401Medium

Exhaust Gas Recirculation (EGR) Flow Insufficient