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 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 .
    • 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 within 2-6 g/s at idle.
    • If the MAF sensor parameter is not within 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
  • Fuel contamination
  • Malfunctioning fuel injectors
  • Missing, loose, or leaking exhaust components from the HO2S forward
  • 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
  • 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

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 within 2-6 g/s at idle.
    • If the MAF sensor parameter is not within 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