P0171

FUEL SYSTEM 1/1 LEAN

For a complete wiring diagramRefer to Section 8W.
Theory of OperationThe fuel feedback system will maintain a stoichiometric fuel/air mixture, 14.7:1, by modifying the injector pulse width according to the oxygen content of the exhaust gas.
The PCM makes short term and long term fuel corrections to maintain stoichiometric fuel/air ratio for best catalytic converter efficiency. Short term fuel correction is based on upstream O2 sensor output and is designed for quick engine response.
The long term fuel correction compensated for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich and lean conditions over a longer period of time.When Monitored:With the engine running in closed loop mode, the ambient/battery temperature above -6.7°C (20°F) and altitude below 2590.8 m (8500 ft).Set Condition:If the PCM multiplies short term compensation by long term adaptive and a certain percentage is exceeded for two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored.
Two Trip Fault. Three good trips to turn off the MIL
Possible Causes

RESTRICTED FUEL SUPPLY LINEFUEL PUMP INLET STRAINER PLUGGEDFUEL PUMP MODULEO2 SIGNAL CIRCUITO2 RETURN CIRCUITO2 SENSOR HEATER OPERATIONO2 SENSORMAP SENSOR OPERATIONECT SENSOR OPERATIONENGINE MECHANICALFUEL FILTER/PRESSURE REGULATOR (HIGH)PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 – ENGINE – DIAGNOSIS AND TESTING).

Diagnostic Test

1. ACTIVE DTCDiagnose all other trouble codes before continuing.Check for contaminants that may have damaged an O2 Sensor: contaminated fuel, unapproved silicone, oil and coolant.Start the engine.Allow the engine to reach normal operating temperature.With a scan tool, select View DTCs.It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze
Frame data.Is the DTC Active or Pending at this time?YesGo To 2NoRefer to the INTERMITTENT CONDITION Diagnostic Procedure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) 2. CHECKING FUEL PRESSURE The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must
be released. Failure to follow these instructions can result in personal injury or death. Install a fuel pressure gauge to the fuel rail.Ignition on, engine not running.With a scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).Turn the ignition off.Choose a conclusion that best matches your fuel pressure reading.Within SpecificationGo To 3Above SpecificationReplace the fuel filter/pressure regulator.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) Below SpecificationGo To 13 Stop All Actuations. 3. CHECKING THE EXHAUST SYSTEM FOR LEAKSTurn the ignition off.Raise the vehicle in accordance with the Service Information.The normal operating temperature of the exhaust system is very high. Never work around or attempt to service any part of the exhaust system until it has cooled. Special
care should be taken when working near the catalytic converter. The temperature of the converter rises to a high level after a short period of engine operating timeConnect Exhaust Cone #8404-EC or #8404–EC to Air Pressure Regulator (with hose) #W-18-MIL-1146AS.The air pressure must not exceed 27.6 kPa (4 psi), otherwise engine damage can occur.Attach shop air to the air pressure regulator.Adjust the Air Pressure Regulator to 27.6 kPa (4 psi)Insert the exhaust cone into the vehicle tail pipe.If the vehicle is equipped with dual exhaust. Use the #8404-ECT with equipped attached plug, plug one side of the dual exhaust pipe. Pressurize the other as described above.Apply SNOOP leak finder liquid or a mixture of liquid dish soap and water to the following areas: – All welded joints from the exhaust manifold to 152.4 mm (6 inches) behind the downstream O2 sensor – O2 sensor seal points – O2 sensor boss welds – Flange/joint connection(s) – Exhaust manifold to cylinder head connection(s) – EGR solenoid gasket base and tube seal points (if equipped)Watch for the liquid/soapy water to bubble.Use the following definitions to help determine if system or component repair/replacement is necessary:Type 1 Leak is defined as a leak where very small foam like bubbles 1 mm (0.04 of an inch) or less appear.Any Type 1 or greater leaks found in welded joints, O2 sensor seal points or O2 sensor boss welds must be repaired or the component must be replaced.Type 2 Leak is defined as a leak where larger bubbles pea size, 8 mm (0.3 of an inch) or greater appear.Any Type 2 or greater leaks found in flange or joint connections, exhaust manifold to cylinder head connections, or EGR gasket and tube seal points must be repaired or the components must be
replaced
Leak LocationRepair required if results at 27.6 kPa (4 psi) reveal bubble size:Welded jointsType 1, 1 mm (0.04 of an inch) or greaterO2 Sensor seal pointsType 1, 1 mm (0.04 of an inch) or greaterO2 Sensor boss weldsType 1, 1 mm (0.04 of an inch) or greaterFlange / joint connectionsType 2, 8 mm (0.3 of an inch) or greaterExhaust Manifold to cylinder head connectionsType 2, 8 mm (0.3 of an inch) or greaterEGR gasket and tube seal pointsType 2, 8 mm (0.3 of an inch) or greater

If a leak is found that matches the above definition, repair or replace the component as necessary.Once the repair is complete, repeat the procedure to verify that all leaks have been repaired.Were any exhaust leaks found?YesRepair or replace the leaking exhaust parts as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE)NoGo To 44. O2 SENSOR OPERATIONStart the engine.Allow the engine to reach normal operating temperature.If one of the O2 Sensor’s Signal or Return circuit is shorted to ground the scan tool will display all O2 Sensor voltage readings low. The O2 Sensor that is shorted
to ground will display a voltage reading near or at 0 volts.If one of the O2 Sensor Signal or Return circuits are shorted to voltage, the scan tool will display all O2 Sensor voltage readings high.After the repairs have been made, verify proper O2 Sensor operation. If all the O2 Sensor voltage readings have not returned to normal, follow the diagnostic procedure
for the remaining O2 Sensors.With a scan tool, monitor all of the O2 Sensor voltage readings.Is the voltage switching between 2.5 and 3.4 volts for all the O2 Sensors?YesGo To 5NoGo To 95. 1/1 O2 SENSOR HEATER OPERATIONTurn the ignition off.Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test. Allow the O2 Sensor voltage to stabilize at 5.0 volts.Ignition on, engine not running.With a scan tool, actuate the 1/1 O2 Heater Test.With the scan tool, monitor 1/1 O2 Sensor voltage for at least 2 minutes.Does the voltage stay above 4.5 volts?YesReplace the 1/1 O2 Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) NoGo To 66. MAP SENSOR OPERATIONIgnition on, engine not running.With a scan tool, read the Barometric Pressure.The Barometric Pressure should be approximately equal to the actual barometric pressure. If necessary, compare the value to the value of a known good vehicle of a similar
make and model.Turn the ignition off.Connect a Vacuum Gauge to a Manifold Vacuum source.Start the engine.Allow the engine to idle.If engine will not idle, maintain a constant RPM above idle.With the scan tool, read the MAP Sensor vacuum value.Is the scan tool reading within 1″ of the Vacuum Gauge reading and the barometric pressure comparable to a know good vehicle?YesGo To 7NoReplace the MAP Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) 7. ECT SENSOR OPERATIONFor this test to be valid, the thermostat must be operating correctly.This test works best if performed on a cold engine (cold soak)Ignition on, engine not running.With a scan tool, read the Engine Coolant Temperature (ECT) Sensor value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere
close to the ambient temperature.If engine coolant temperature is above 82° C (180° F), allow the engine to cool until 65° C (150° F) is reached.Start the Engine.During engine warm-up, monitor the ECT Sensor value. The temperature value change should be a smooth transition from start up to normal operating temperature 82° C (180° F). The value
should reach at least 82° C (180° F).Did the ECT value increase smoothly and did it reach at least 82° C (180° F)?YesGo To 8NoReplace the Engine Coolant Temperature Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) 8. ENGINE MECHANICALTurn the ignition off.Check for any of the following conditions/mechanical problems.AIR INDUCTION SYSTEM – must be free from leaks.ENGINE VACUUM – must be at least 13 inches in neutralENGINE VALVE TIMING – must be within specificationsENGINE COMPRESSION – must be within specificationsENGINE EXHAUST SYSTEM – must be free of any restrictions or leaks.ENGINE PCV SYSTEM – must flow freelyTORQUE CONVERTER STALL SPEED – must be within specificationsPOWER BRAKE BOOSTER – no internal vacuum leaksFUEL – must be free of contaminationFUEL INJECTOR – plugged or restricted injector; control wire not connected to correct injectorAre there any engine mechanical problems?YesRepair as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) NoGo To 129. 1/1 O2 SENSOR

Ignition on, engine not running.Disconnect the 1/1 O2 Sensor harness connector.With a scan tool, monitor the 1/1 O2 Sensor voltage.O2 Sensor voltage should read 5.0 volts on the scan tool with the connector disconnected.Connect a jumper wire between the (K41) Signal circuit and the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.The voltage should drop from 5.0 volts to 2.5 volts with the jumper wire in place.Did the O2 Sensor voltage change from 5.0 volts to 2.5 volts with the jumper wire installed?YesReplace the O2 Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE)NoGo To 10Remove the jumper wire before continuing.10. (K41) O2 SENSOR 1/1 SIGNAL CIRCUITWith a scan tool, monitor the 1/1 O2 Sensor voltage reading with the jumper wire removed.The scan tool will display all O2 Sensor voltage readings approximately 5.0 volts when only one O2 Sensor’s Signal circuit is shorted to voltage.The scan tool will display one O2 Sensor voltage close to zero and the others will read lower than normal when one O2 Sensor Signal circuit contains excessive resistance.Is the voltage above 4.8 volts?YesGo To 11NoCheck the (K41) O2 Sensor 1/1 Signal circuit for a short to ground, open, or short to voltage. Inspect the O2 Sensor connector and the PCM harness connector.
If OK, replace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) 11. (K902) O2 RETURN UPSTREAM CIRCUIT

Disconnect the 1/1 O2 Sensor harness connector.Measure the voltage on the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.Is the voltage at 2.5 volts?YesGo To 12NoCheck the O2 Return circuit for a short to ground, open, or short to voltage. Inspect the O2 Sensor connector and the PCM harness connector. If OK, replace
and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) 12. PCMBefore continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.Were there any problems found?YesRepair as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) NoReplace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) 13. RESTRICTED FUEL SUPPLY LINE The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must
be released. Failure to follow these instructions can result in personal injury or death. Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.Install special 5/16 fuel line adapter tool #6539 between disconnected fuel line and the fuel pump module.Attach a fuel pressure test gauge to the T fitting on tool #6539.Ignition on, engine not running.With a scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).Is the fuel pressure within specification?YesRepair or replace fuel supply line as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) NoGo To 14Stop All Actuations. 14. FUEL PUMP INLET STRAINERThe fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must
be released.Turn the ignition off.Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer.Is the Fuel Inlet Strainer plugged?YesReplace the Fuel Pump Inlet Strainer.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE) NoGo To 1515.FUEL PUMP MODULEIf there are no possible causes remaining, view repair.RepairReplace the Fuel Pump Module.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 – ENGINE – STANDARD PROCEDURE)