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john -aka eauto
john -aka eauto, The Car Guy
Category: Saturn
Satisfied Customers: 15999
Experience:  ase tech 15 + years foreign domestic & european
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Engine light keeps..light keeps coming..the 02 senor changed

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Engine light keeps coming on. Got the 02 senor changed. Good for 3 or 4 days. checked and blew out everything light goes off for a week. Back on. Back and forth with this problem. Got it taking care of and went to get it smog tested. passed on everything except functional check due to warning lamp failure. Light back on. Went to my mechanic he got the light to go off but he said he got the code reading PO171 again. What is wrong with this car? Saturn wants $105 just to check and tell me whats wrong. Thats a lot of money it it is going to happen again.
Hi . Thank you for asking your question on JustAnswer. here ya go...

DTC P0171

The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent . If the HO2S indicates a rich condition, the FT values will be below 0 percent . The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. If the ECM detects an excessively lean condition, DTC P0171 sets.

This diagnostic procedure supports the following DTC:
DTC P0171 Fuel Trim System Lean


  • DTCs P0030, P0036, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0201-P0204, P0300, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0506, P0507, P1106, P1107, P1133, P1134 are not set.
  • The engine is in CL status.
  • The engine coolant temperature (ECT) is between -40 and +127°C (-40 and +260.6°F) .
  • The intake air temperature (IAT) is more than -20°C (-4°F) .
  • The manifold absolute pressure (mao) is more than 5 kPa (0.7 psi).
  • The vehicle speed is less than 134 km/h (83 mph) .
  • The engine speed is between 400-6,000 RPM .
  • The mass air flow (MAF) is more than 0.5 g/s .
  • The barometric pressure (BARO) is more than 70 kPa (10.2 psi) .
  • The fuel level is more than 10 percent .
  • DTC P0171 runs continuously once the above conditions have been met.


  • The long term FT weighted average value is more than a calibrated value.
  • The above condition is present for more than 2 minutes .


  • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
  • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.


  • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
  • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
  • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
  • Clear the mil and the DTC with a scan tool.


  • Test for fuel contamination. Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool).
  • The system will go lean if an injector is not supplying enough fuel.
  • A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel, a plugged fuel filter, or a restricted fuel pipe.
  • Review the Failure Records with a scan tool. If an intermittent condition is suspectedgraphicgraphic

Thank you again for trusting us with your problem. John aka eauto
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Customer: replied 6 years ago.
I'm female and have no idea what all this means. I printed everything out to give my mechanic but I still don't know what is wrong.
its needs to be further diagnosed..It could be weak fuel pressure, a dirty or failed mass air flow sensor, a failed or weak fuel pump , a vacum or intake leak or a clogged fuel filter
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