For a complete wiring diagram Refer to Section 8W.For an aged O2 sensor, the response rate to the air/fuel change is slower than when it was new. The O2 sensor tends to move less with the same air/fuel changes in a given time frame. Therefore by observing the activity of voltage readings from the upstream O2 sensor, the quality of the O2 sensor can be detected.When Monitored:Vehicle is started and driven between 32 and 88.5 km/h (20 and 55 mph) with the Throttle open for a minimum of 120 seconds. Coolant greater than 70° C (158° F). Catalytic Converter Temp greater than 600° C (1112° F) and EVAP Purge is active.Set Condition:O2 Sensor response is too slow for a calibrated amount of time. Two Trip Fault. Three good trips to turn off the MIL.Possible CausesEXHAUST LEAK(K41) O2 1/1 SIGNAL CIRCUIT(K902) O2 RETURN UPSTREAM CIRCUITO2 SENSORAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. ACTIVE DTCCheck for contaminants that may have damaged the O2 Sensor: contaminated fuel, unapproved silicone, oil and coolant.Ignition on, engine not running.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.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 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 replacedLeak 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 greaterIf 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 33. (K41) O2 1/1 SIGNAL CIRCUIT

Turn the ignition offDisconnect the 1/1 O2 Sensor harness connector.Ignition on, engine not running.Measure the voltage on the (K41) O2 1/1 Signal circuit in the O2 Sensor harness connector.Is the voltage between 4.5 and 5.0 volts?YesGo To 4NoCheck the (K41) O2 1/1 Signal circuit for a short to ground, open, or short to voltage. If OK, replace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 4. (K902) O2 RETURN UPSTREAM CIRCUIT

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 5NoCheck the (K902) O2 Return Upstream circuit for a short to ground, open, or short to voltage. If OK, replace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 5. O2 SENSOR If there are no possible causes remaining, view repair.RepairReplace the O2 SensorPerform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)