Circuit/System Testing: P0171

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The value should be less than approximately 19.5 percent with the engine running at operating temperature.

• If the value is not less than 19.5 percent, inspect for the following:

• With the ignition ON and the engine OFF, 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 and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19-42 kPa.
  • If the MAP sensor parameter is not between 19-42 kPa, refer to DTC P0106 .
• With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be between 3-10 g/s at idle.
  • If the MAF sensor parameter is not between 3-10 g/s at idle, refer to DTC P0101  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 .
• Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) .
• Ethanol concentration greater than 15 percent-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) .
• Malfunctioning fuel injectors-Refer to Fuel Injector Diagnosis (w/J39021 or Tech 2) or Fuel Injector Diagnosis (w/CH47976) .
• Missing, loose, or leaking exhaust components from the HO2S forward-Refer to Symptoms - Engine Exhaust .
• Vacuum leaks at the intake manifold, the throttle body, the brake booster hose, 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 .
• 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
• The HO2S sensor 1 low signal circuit for an open circuit or high resistance
• Malfunctioning engine components-Refer to Symptoms - Engine Mechanical .

Repair or replace as necessary.