For a complete wiring diagram Refer to Section 8W.The fuel feedback system will maintain a stoiciometric fuel/air mixture, 14.7:1, by modifying the injector pulsewidth according to the oxygen content of the exhaust gas. The PCM makes short term and long term fuel corrections to maintain stoiciometric 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 purge fuel multiplier and the result is below a certain value for 30 seconds over 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 CausesO2 SENSOR HEATER OPERATIONEVAP PURGE SOLENOID OPERATIONO2 SIGNAL CIRCUITO2 RETURN CIRCUITO2 SENSOR MAP SENSORECT SENSORENGINE MECHANICALFUEL FILTER/PRESSURE REGULATOR (HIGH)PCMAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).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 PRESSUREThe 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 the 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) Stop All Actuations. 3. O2 SENSOR OPERATIONStart the engine.Allow the engine to reach normal operating temperature.If one of the O2 Sensors Signal or Return circuit is shorted to ground or voltage, all the other O2 Sensor voltage readings will be affected.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 the scan tool, monitor the 1/1 O2 Sensor voltage reading.Is the voltage switching between 2.5 and 3.4 volts?YesGo To 4NoGo To 94. 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 the scan tool, perform the 1/1 O2 Heater Test.With the scan tool, monitor the O2 Sensor voltage while performing the Heater test for at least 2 minutes.Does the voltage stay above 4.5 volts during the Heater test?YesReplace the O2 Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 5 5. 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 Barometric Pressure value of this vehicle 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 a scan tool, read the MAP Sensor vacuum value.Is the scan tool reading for MAP Vacuum within 1 inch of the Vacuum Gauge reading and is the Barometric Pressure reading of the vehicle the approximately the same as actual Barometric Pressure?YesGo To 6NoReplace the MAP Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) Remove the vacuum gauge before continuing.6. 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 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 Engine Coolant Temperature value. The temp value change should be a smooth transition from start up to normal operating temp 82° C (180° F). The value should reach at least 82° C (180° F).Did the ECT value increase smoothly and reach at least 82° C (180° F)?YesGo To 7NoReplace the Engine Coolant Temperature Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 7. EVAP PURGE SOLENOID OPERATIONTurn the ignition off.Disconnect the hoses at the Evap Purge Solenoid.Using a hand vacuum pump, apply 10 inches of vacuum to the Evap Purge Solenoid vacuum source port on the component side.Did the Evap Purge Solenoid hold vacuum?YesGo To 8NoReplace the EVAP Purge Solenoid.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) Connect the vacuum hoses before continuing.8. ENGINE MECHANICALCheck for any of the following conditions/mechanical problems.AIR INDUCTION SYSTEM - must be free from restrictions.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

Perform the following test on the O2 Sensors whose voltage was not switching properly in the previous step.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) O2 Sensor 1/1 Signal circuit and the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.The voltage should drop from 5.0 volts down to 2.5 volts with the jumper wire connected.Did the O2 Sensor voltage drop from 5 volts to 2.5 volts when the jumper wire was installed?YesReplace the 1/1 O2 SensorPerform 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 CIRCUIT

When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.Start the engine.Measure the voltage on the (K41) O2 Sensor 1/1 Signal circuit in the O2 Sensor harness connector.Is the voltage above 4.8 volts?YesCheck the (K41) O2 Sensor 1/1 Signal circuit for damage, 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) NoGo To 1111. (K902) O2 SENSOR RETURN UPSTREAM CIRCUIT

Engine still running.Measure the voltage on the (K902) O2 Return Upstream circuit in the 1/1 O2 Sensor harness connector.Is the voltage at 2.5 volts?YesGo To 12NoCheck the (K902) O2 Return Upstream circuit for damage, 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) Turn the ignition off before continuing.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)