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EGR System Diagnosis

  1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES article.
  2. Set parking brake and block wheels. Connect scan tool to data link connector. Start engine and let idle until normal operating temperature is obtained. Using scan tool, command EGR pintle position to zero percent. Increase engine speed to 2000 RPM. If EGR pintle position is now less than 3 percent, go to next step. If EGR pintle position is now greater than 3 percent, go to step 14).
  3. Using scan tool, command EGR pintle position to 100 percent in 10 percent increments. Observe MAP sensor and actual EGR pintle position at each increment. EGR pintle should increase by 25 percent or commanded value and MAP sensor value should also increase. If the actual EGR position is within 25 percent of commanded value within 3 seconds, go to next step. If the actual EGR position is not within 25 percent of commanded value within 3 seconds, go to step 6).
  4. Using scan tool, set EGR pintle position to 25 percent. If MAP sensor value increases, go to next step. If MAP sensor value does not increase, go to step 13).
  5. Using scan tool, command EGR pintle position to 100 percent. If actual EGR pintle position is 100 percent, go to step 15). If actual EGR pintle position is not 100 percent, go to step 14).
  6. Check fuses. If fuses are okay, go to next step. If any fuse(s) is blown, repair as necessary and go to step 15).
  7. Check EGR valve circuits for opens between PCM and EGR valve harness connectors. If open does not exist, go to next step. If open exists, repair as necessary and go to step 15).
  8. Check for poor connection at EGR valve. If poor connection does not exist, go to next step. If poor connection exists, repair as necessary and go to step 15).
  9. Measure voltage at EGR valve reference voltage circuit (Red wire) at EGR valve harness connector. See Fig 1. If 5 volts exists, go to next step. If 5 volts does not exist, go to step 11).
  10. Turn ignition switch to RUN position. Remove EGR valve, leaving harness connector attached. Push EGR pintle in and hold pintle in. Using a voltmeter, backprobe sensor signal circuit (Brown wire) at EGR valve harness connector. If no voltage exists, go to next step. If any voltage exists, go to step 14).
  11. Check EGR valve pintle signal circuit (Brown wire) for open between PCM and EGR valve harness connector. If open does not exist, go to next step. If open exists, repair as necessary and go to step 15).
  12. Replace PCM. Program PCM, perform VTD password relearn procedure and perform crankshaft variation learn procedure. After repair is complete, go to step 15).
  13. Clean EGR passages and go to step 15).
  14. Replace EGR valve and go to next step.
  15. Turn ignition switch to RUN position. Using scan tool, command EGR valve on then off. If EGR valve operates properly, system is okay at this time. If EGR valve does not operate properly, go to step 2).
Fig 1: Identifying EGR Valve Harness Connector Terminals
G98E00871Courtesy of GENERAL MOTORS CORP.
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