For a complete wiring diagram Refer to Section 8W.Exhaust gas recirculation is a method of reducing emissions of oxides of nitrogen. As the inert exhaust gas is recirculated, the mixture absorbs heat in the combustion chamber without interacting with the fuel/air mixture and reduces the formation of NOx emissions. After the EGR monitor conditions are met, the EGR valve is turned on and off momentarily. The EGR monitor calculated the difference in engine roughness from the EGR off condition to the EGR condition. This engine combustion stability difference as measured by engine roughness is the measure of a functional EGR system.When Monitored:Engine running for greater than two minutes with the Engine Coolant Temp greater than 70°C (158°F). EGR active. Less than 8500 feet. Ambient temperature greater than -6°C (20°F).Set Condition:The PCM closes the EGR valve while monitoring the O2 Sensor signal. Once a closed EGR fueling sample has been established the PCM then ramps in EGR and additional fueling while monitoring the O2 sensor signal in the open state. A fueling sample is again established. The PCM then compares the different O2 Sensor signal readings (fueling samples). If a larger than expected variation is detected, a soft failure is recorded. Three soft failures set a one trip failure. After two failed trips, a DTC is set and the MIL is illuminated.Possible Causes(Z906) EGR SOLENOID GROUND CIRCUIT OPEN(K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO GROUND(K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO BATTERY VOLTAGE(K35) EGR SOLENOID CONTROL CIRCUIT OPENEGR SOLENOID ASSEMBLYPCMAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. ACTIVE DTCStart 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. EGR OPERATIONIf the vehicle is running rough at idle (scan tool not actuating) follow the yes path to continue.Turn all accessories off.Start the engine.Allow the engine to reach normal operating temperature.With the scan tool, enter Engine System Test, then EGR System Test.Actuate the FLOW function in the EGR System Test.Did the engine run rough or stall?YesGo To 3NoGo To 63. EGR VALVE OPEN AT IDLETurn the ignition off.Disconnect the EGR Solenoid Assembly harness connector.Start engine. Attempt to allow the engine to idle.Does the engine run rough or stall?YesInspect the EGR tube assembly. If OK, replace the EGR valve.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 44. EGR VALVE ASSEMBLY INSPECTIONInspect the EGR Assembly for the following.Gasket(s) for leakingDamage and/or holes in the EGR tube(s)Carbon build up on or near the EGR pintle and passage ways.Obstruction in the EGR tubes.Were any problem found?YesRepair or replace the EGR Assembly as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 55. (K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO BATTERY VOLTAGE

Turn the ignition off.Disconnect the EGR Solenoid harness connector.Ignition on, engine not running.Measure the voltage on the (K35) EGR Solenoid Control circuit in the EGR Solenoid connector.Is the voltage above 1.0 volt?YesRepair the short to battery voltage in the (K35) EGR Solenoid Control circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 106. EGR SOLENOID ASSEMBLY

Disconnect the EGR Solenoid harness connector.Using a 12-volt test light, jump across the (K35) EGR Solenoid Control terminal and the (Z906) Ground terminal in the EGR Solenoid harness connector.With the scan tool, actuate the EGR solenoid.Does the 12-volt test light flash on and off?YesInspect the tube(s) for obstructions and damage, repair as necessary. If OK, replace the EGR Solenoid Assembly.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 77. (Z906) EGR SOLENOID GROUND CIRCUIT OPEN

Turn the ignition off.Using a 12-volt test light connected to battery voltage, probe the (Z906) EGR Solenoid ground circuit in the EGR Solenoid harness connector.Does the 12-volt test light illuminate brightly?YesGo To 8NoRepair the open in the (Z906) EGR Solenoid ground circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 8. (K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO GROUND

Disconnect the C2 PCM harness connector.Measure the resistance between ground and the (K35) EGR Solenoid Control circuit in the EGR Solenoid harness connector.Is the resistance below 100 ohms?YesRepair the short to ground in the (K35) EGR Solenoid Control circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 99. (K35) EGR SOLENOID CONTROL CIRCUIT OPEN

Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.Measure the resistance of the (K35) EGR Solenoid Control circuit from the EGR Solenoid harness connector to the appropriate terminal of special tool #8815.Is the resistance below 5.0 ohms?YesGo To 10NoRepair the open in the (K35) EGR Solenoid Control circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 10. 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)