Circuit/System Testing: P0171

Allow the engine to reach operating temperature. With the engine running, observe the Long Term FT parameter with a scan tool. The reading should be between 0-20 percent.

• If not within the specified range, inspect for the following:

• Ignition ON, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .
  • If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106 .
• With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be between 2-6 g/s at idle.
  • If the MAF sensor parameter is not between 2-6 g/s at idle, refer to DTC P0101 or P1101  or DTC P0102 or P0103 .
• Vacuum hoses for splits, kinks, and improper connections
• Insufficient fuel in the tank
• Low fuel pressure - Refer to Fuel System Diagnosis (Except Saturn) or Fuel System Diagnosis (Saturn) .
• Ethanol concentration greater than 15 percent - Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• Malfunctioning fuel injectors - Refer to Fuel Injector Diagnosis (J39021 or Tech 2) or Fuel Injector Diagnosis (CH47976) or Fuel Injector Diagnosis (SA9182E or Tech 2) .
• Missing, loose, or leaking exhaust components from the HO2S forward - Refer to Symptoms - Engine Exhaust .
• Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
• The air induction system and the air intake ducts for leaks or for a missing air filter element
• A cracked EVAP canister
• Evaporative pipes obstructed or leaking
• The crankcase ventilation system for leaks - Refer to Crankcase Ventilation System Inspection/Diagnosis (Without Turbocharger) .
• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
• The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit
• Malfunctioning engine components - Refer to Symptoms - Engine Mechanical .