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 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, P0107, or P0108 .
  • With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 3-10 g/s at idle.
    • If the MAF sensor parameter is not within 3-10 g/s at idle, refer to DTC P0101 or P1101  or DTC P0102 or P0103 .
  • Vacuum hoses for splits, kinks, and proper connections
  • Sufficient fuel in the tank
  • Low fuel pressure
  • Fuel contamination
  • Properly functioning fuel injectors
  • Missing, loose, or leaking exhaust components from the HO2S forward
  • Vacuum leaks at the intake manifold, the throttle body, 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
  • Evaporative canister purge lines plugged or obstructed
  • The crankcase ventilation system for leaks
  • The HO2S for proper 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

P0172

• 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 more than -25 percent with the engine running at operating temperature.
• If the value is not more than -25 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, P0107, or P0108 .
  • With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 3-10 g/s at idle.
    • If the MAF sensor parameter is not within 3-10 g/s at idle, refer to DTC P0101 or P1101  or DTC P0102 or P0103 .
  • Vacuum hoses for splits, kinks, and proper connections
  • The inlet screen of the MAF sensor for blockage
  • A malfunctioning MAF-Refer to DTC P0068 or P0121  or DTC P0101 or P1101 .
  • The air duct for being collapsed or restricted
  • The air filter for being dirty or restricted
  • Objects blocking the throttle body
  • Excessive fuel in the crankcase
  • A saturated evaporative canister, a stuck purge valve, or the fuel cap not sealing
  • The evaporative emissions control system for proper operation
  • Excessive fuel pressure
  • Properly functioning fuel injectors
  • Fuel contamination
  • The HO2S for proper installation and for electrical wires or connectors that may have contacted the exhaust system
  • The HO2S signal circuit shorted to voltage