Circuit/System Testing: P0171: P0172

Allow the engine to reach operating temperature. With the engine running, observe the Long Term FT parameter with a scan tool. The value should be more than approximately -20 percent with the engine running at operating temperature.

• If the value is not more than -20 percent, inspect for the following:

• 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 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
• The air intake duct for being collapsed or restricted
• The air filter for being dirty or restricted
• Objects blocking the throttle body
• Excessive fuel in the crankcase due to leaking fuel injectors
• The evaporative emissions control system for improper operation
• Excessive fuel pressure
• Malfunctioning fuel injectors
• Fuel contamination
• The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
• The HO2S signal circuit shorted to voltage