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Home >> GMC >> 2003 >> Envoy RWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures - 4.2L >> Ignition Systems >> Electronic Ignition System >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK -- ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After performing diagnostic system check, go to next step.
  2. Are DTCs P0335 or P0336 set? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no DTC(s) are set, go to next step.
  3. Attempt to start engine. Does engine start and run? If yes, go to next step. If no, go to step  15.
  4. Observe Misfire Current Counters parameter with a scan tool. Does scan tool display any Misfire Current Counters incrementing? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. Remove ignition coil for affected cylinder. Install Spark Tester (J-26792) to spark plug boot. Attach tester to a good engine ground. Observe spark tester. Crank engine. Does spark jump tester gap? If yes, go to step  11. If no, go to next step.
  6. Turn ignition off. Disconnect ignition coil for misfiring cylinder. Turn ignition on, with engine off. Probe ignition 1 voltage circuit of affected ignition coil with a test light connected to good ground. See Figure. Does test light illuminate? If yes, go to next step. If no, go to step  15.
  7. Probe ignition 1 voltage circuit of affected ignition coil with a test light connected to ignition coil ground circuit. Does test light illuminate? If yes, go to next step. If no, go to step  16.
  8. Start engine. Measure frequency from IC control circuit of respective ignition coil to a good ground. Does frequency measure within 2-20 Hz? If yes, go to step  14. If no, go to next step.
  9. Turn on ignition, with engine off. Measure voltage from IC control circuit of respective ignition coil to a good ground with a DVOM. Does voltage measure more than one volt? If yes, go to step  17. If no, go to next step.
  10. Test IC control circuit for an open, short to ground or high resistance. Did you find and correct condition? If yes, go to step  21. If no, go to step  13.
  11. Exchange spark plug with a spark plug from a non misfiring cylinder. Install ignition coil. Start engine. Does scan tool display that misfire followed that spark plug? If yes, go to step  20. If no, go to next step.
  12. Inspect insulating spark plug boot and conducting spring for any contamination, deterioration or arching. Did you find and correct condition? If yes, go to step  21. If no, diagnose for an engine mechanical problem.
  13. Test for an intermittent and for a poor connection at PCM. Did you find and correct condition? If yes, go to step  21. If no, go to step  19.
  14. Test for an intermittent and for a poor connection at ignition coil. Did you find and correct condition? If yes, go to step  21. If no, go to step  18.
  15. Repair open or short to ground in ignition 1 voltage circuit. See Figure. After repairs, go to step  21.
  16. Repair open in ignition coil ground circuit. After repairs, go to step  21.
  17. Repair short to voltage in IC control circuit. After repairs, go to step  21.
  18. Replace ignition coil. After replacing ignition coil, go to step  21.
  19. Replace PCM. Refer to REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After replacing PCM, go to step  21.
  20. Replace spark plug. After replacing spark plug, go to next step.
  21. Start engine. Does engine start and run? If yes, go to next step. If no, go to step  2.
  22. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Let engine reach operating temperature. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If no DTC(s) are set, system is okay.
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