P0171
DTC P0171CIRCUIT DESCRIPTION
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. During Open Loop the ECM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop the ECM adds oxygen sensor inputs to calculate fuel trim. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. Short Term Fuel Trim (FT) values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term FT values change slower in response to trends in Short Term FT adjustments. This DTC is continuously monitored during engine operation. If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets.
CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141 are not set.
- The system is in Closed Loop status.
- Fuel trim is enabled.
- The fuel level is more than 10 percent.
CONDITIONS FOR SETTING THE DTC
- The LT FT Cruise/Acce parameter is above 23 percent.
OR
- The LT FT Idle/Decel. parameter is above 8.5 percent.
ACTION TAKEN WHEN THE DTC SETS
- 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.
CONDITIONS FOR CLEARING THE MIL/DTC
- 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.
DIAGNOSTIC AIDS
- A skewed mass air flow (MAF) sensor may set this DTC. Refer to DTC P0101. P0101
- The system will go lean if an injector is not suppling enough fuel.
- The system will go lean during high fuel demand.
- Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions. Diagnostic Strategies
TEST
