P0171

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) 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 PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed loop the PCM adds oxygen sensor inputs to calculate short term and long term fuel trim, fuel delivery adjustments. 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 values change rapidly in response to the HO2S voltage signals. Long Term fuel trim makes coarse adjustments in order to maintain Air/Fuel Ratio of 14.7:1. If the PCM detects an excessively lean condition, this DTC will set.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0107, P0108, P0121. P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0300, P0401, P0403, P0404, P0405, P0410, P0440, P0442, P0446, P0506, P0507, P1404 or P1441 are not set.
^ The Engine Coolant Temperature (ECT) is between 20°C-110°C (68°F-230°F).
^ The intake air temperature is between -18°C and +76°C (-4°F and +168°F).
^ The Manifold Absolute Pressure (MAP) is between 15-85 kPa (2.1-12.3 psi).
^ The vehicle speed is less than 132 km/h (82 mph).
^ The engine speed is between 575-4,000 RPM.
^ The barometric pressure is more than 70 kPa (10.1 psi).
^ The mass airflow (MAF) is between 3.0 g/s and 85 g/s.
^ The fuel level is more than 10 percent.

CONDITIONS FOR SETTING THE DTC
The average long term fuel trim value is above 23 percent. All of the above conditions are present for 6 seconds.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after the third consecutive trip the diagnostic has run and passed.
^ The history DTC will clear if the fault conditions have not been detected for 40 warm-up cycles.
^ A scan tool can be used to clear DTC information.

ACTION TAKEN WHEN THE DTC SETS
^ First failure:
- The MIL is not turned ON.
- A DTC is stored in memory under Failed Last Test.
- The Failure Records are stored.
^ Second consecutive drive cycle with a failure:
- The MIL is turned ON.
- A DTC is stored in memory under history.
- The Freeze Frame data is stored.
- The Failure Records are stored.

DIAGNOSTIC AIDS
^ The system will go lean if an injector is not supplying enough fuel.
^ The system will go lean during high fuel demand.
^ Using a scan tool, review the Failure Records. If an intermittent condition is suspected, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-2:

Steps 3-8:

The numbers below refer to the step numbers on the diagnostic table.
5. If no problem was found, refer to Fuel System Diagnostics for a possible fuel problem. Component Tests and General Diagnostics
6. If no problems are found, a worn cam, worn intake or exhaust values or other engine mechanical failures may be at fault.