DTC P0171: 1/1 Fuel System Lean: Description

Fuel system lean condition is monitored with engine running in closed loop mode, ambient/battery temperature at more than 20°F (-6.7°C), and at altitude less than 8000 feet. DTC will set in Powertrain Control Module (PCM) memory when PCM senses fuel system is running too lean on 2 sequential trips. Also, freeze frame data will be stored and MIL will illuminate. Possible causes are: restricted fuel supply line, fuel pump inlet strainer plugged, defective fuel pump module, defective 1/1 Heated Oxygen Sensor (HO2S), 1/1 HO2S signal circuit shorted to ground, improper 1/1 HO2S heater operation, Throttle Position (TP) sensor voltage more than .92 volt with throttle closed, defective TP sensor, defective Manifold Absolute Pressure (MAP) sensor, defective Engine Coolant Temperature (ECT) sensor, engine mechanical problem or defective fuel filter/pressure regulator.