For a complete wiring diagram Refer to Section 8W.The State of Change (SOC) catalyst monitor uses the signals from both the upstream and downstream O2 sensors to detect aging of the catalyst. Based on the fact that when a catalyst ages, it loses some of its Oxygen Storage Capacity (OSC). As a result, part of the untreated exhaust gases can breakthrough the catalyst and causes the downstream O2 sensor to deviate from its neutral (Stoichiometric) position. By observing the activities in the downstream O2 signal, the degradation level of catalyst can be detected. In general, the higher the downstream O2 sensor SOC value, the more exhaust gas breakthrough and the lower the OSC of the catalytic converter.When Monitored:The monitor will run at between 1400 and 2300 RPM. It also runs between 40 and 70 kPa.Set Condition:If the final State of Change index is within the calibrated fail threshold. Two trip fault. Three good trips to turn off the MIL.Possible CausesEXHAUST LEAKENGINE MECHANICALAGING O2 SENSORCATALYTIC CONVERTERAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. ACTIVE DTCA new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set. Review the repair history of the vehicle before continuing.If an O2 Sensor DTC set along with the Catalytic Converter Efficiency DTC diagnose the O2 Sensor DTC(s) before continuing.Check for contaminants that may have damaged the O2 Sensor and Catalytic Converter: contaminated fuel, unapproved silicone, oil and coolant, repair necessary.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. VISUALLY INSPECT CATALYTIC CONVERTERInspect the Catalytic Converter for the following damage.Damaged Catalytic Converter, dents or holes.Severe discoloration caused by overheating the Catalytic Converter.Catalytic Converter broken internally.Inspect both ends of the converter, inlet and outlet.Leaking Catalytic Converter.Were any problems found?YesReplace the Catalytic Converter. Repair the condition that may have caused the failure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 33. 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 44. ENGINE MECHANICALCheck the exhaust for excessive smoke caused by an internal problem in the engine.Is an engine mechanical condition present?YesRepair the engine mechanical condition as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 55. AGING O2 SENSORA new rear O2 Sensor along with an aging front O2 Sensor may cause the DTC to set.Review the vehicles repair history.Has the rear O2 Sensor been replaced without replacing the front O2 Sensor?YesReplace the 2/1 O2 Sensor as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 66. CATALYTIC CONVERTERIf there are no possible cause remaining, view repair.RepairReplace the Catalytic Converter.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)