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Home >> Chevrolet >> 2008 >> Optra5 LS, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls And Fuel - 1.6L >> Diagnostic Information and Procedures >> DTC P0171 or P0172 >> Circuit/System Verification
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Circuit/System Verification

  1. Engine running, observe the DTC information with a scan tool. If there are other DTCs set besides DTC P0171 or P0172, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnose the applicable DTC.
  2. Ignition ON, observe the scan tool manifold absolute pressure (MAP) sensor pressure parameter and compare the reading on the scan tool to the barometric pressure table.
    • If the MAP sensor pressure is not within the range specified for your altitude, refer to DTC P0107 or P0108 .
  3. Engine running, observe the scan tool TP sensor percentage parameter. The reading should be less than 10 percent.
  4. Observe the scan tool HO2S sensor voltage parameter. The reading should fluctuate within 200-800 mV.
    • If out of the specified range, refer to DTC P0131 or P0138, and DTC P0133 .
  5. Engine at normal operating temperature, observe the scan tool Short Term FT parameter. The reading should be between -5 to +5 percent.
    • If not within the specified range, verify none of the following conditions exist:
      • Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
      • Splits, kinks, or improper connections at the vacuum hoses
      • The fuel system is operating lean or rich. Refer to Fuel System Diagnosis .
      • The fuel injectors are operating lean or rich. Refer to Fuel Injector Balance Test with Special Tool .
      • Missing, restricted, or leaking exhaust components-Refer to Symptoms - Engine Exhaust .
      • Vacuum leaks at the intake manifold, throttle body, and injector O-rings - P0171
      • Leaking crankcase ventilation system - P0171
      • The air intake duct for being collapsed or restricted possibly by a restricted air filter - P0172
      • Restricted air cleaner element - P0172
      • Leaking fuel pressure regulator-Inspect for evidence of fuel in the vacuum line. Refer to Fuel System Diagnosis  - P0172.
      • Excessive fuel in the crankcase - P0172
      • The incorrect operation of the EVAP control system - P0172
  6. If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical .
  7. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
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