P0171 or P0174: Notes

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 20 percent with the engine running at operating temperature.

• If the value is not less than 20 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 .
  • Refer to DTC P0106  if the MAP sensor does not indicate the correct barometric pressure.
• With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2-6 g/s at idle.
  • Refer to DTC P0101 or P1101  or DTC P0102 or P0103  if the MAF sensor parameter is not within 2-6 g/s at idle.
• Vacuum hoses for splits, kinks, and improper connections
• Insufficient fuel in the tank
• Low fuel pressure-Refer to Fuel Pump Electrical Circuit Diagnosis .
• Fuel contamination-Refer to Evaporative Emission System Diagnosis .
• Malfunctioning fuel injectors-Refer to Symptoms - Engine Exhaust .
• 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-Refer to Fuel Hose/Pipes Routing Diagram .
• The crankcase ventilation system for leaks
• 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 .