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Ignition System

  1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . After performing OBD system check, go to next step.
  2. Install Tech 1 scan tool. Using scan tool, select FAILED LAST TST function. If Diagnostic Trouble Code (DTC) P0123, P0506/P0507, P0601/P0602 or P1200 is present, diagnose DTC. See TESTS W/CODES article. If DTC(s) are not present, go to next step.
  3. Turn ignition off. Install fuel pressure gauge. Turn ignition on and observe fuel pressure. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm2 ). If fuel pressure is as specified, go to step 5). If fuel pressure is not as specified, go to next step.
  4. If fuel pressure is present, but not as specified, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS  . If fuel pressure is not present, see FUEL SYSTEM.
  5. Check fuel injector feed circuit fuse. If fuse is faulty, check for a shorted circuit or injector. Repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If circuit and injector are okay, go to next step.
  6. Check for open in fuel injector feed circuit or poor connection at injector/engine harness. Repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If circuit or connection is okay, go to step 7).
  7. Turn ignition off. Disconnect 10-pin fuel injector/engine harness connector. Using a test light connected to battery voltage, probe each injector driver circuit while cranking engine. If test light flashes, go to step 9). If test light does not flash, go to next step.
  8. Check for open fuel injector driver circuit(s). Check for poor PCM connector. Repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If circuit or connector is okay, go to step 29).
  9. Remove fuel injection fuse from underhood fuse block. Install Spark Tester (ST-125) to cylinder No. 2, 4 and 6 (one at a time). Connect the spark plug wire of companion cylinder to ground. Crank engine and observe spark tester. If spark is present, go to step 21). If spark is not present, go to next step.
  10. If spark is not present on all coils, go to next step. If spark is not present only on some coils, go to step 16).
  11. Check fuse to Ignition Control Module (ICM) ignition feed circuit. If fuse is faulty, check for short between ICM feed circuit and engine ground, module ground, IC control circuit or reference low circuit. Repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If fuse is okay, go to next step.
  12. Check for open in ICM feed and ground circuit. Repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If circuit is okay, go to next step.
  13. Disconnect 7X Crankshaft Position (CKP) sensor connector from ICM. Using a DVOM, connect DVOM between CKP sensor harness connector terminals. See Fig 1 . Set DVOM to 2-volt AC scale. Crank engine and observe DVOM. DVOM should read about 2-volts AC. If voltage is as specified, go to step 15). If voltage is not as specified, go to next step.
  14. Turn ignition off. Check 7X CKP sensor circuit for open or short to voltage or ground. Check for poor 7X CKP sensor connection. Repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  .
  15. Check for poor ICM connection. Repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If connection is okay, go to step 28).
  16. Check secondary resistance to ignition coil that did not produce a spark. Resistance should be 5000-8000 ohms. If resistance is not as specified, replace ignition coil. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If coil resistance is as specified, go to next step.
  17. Remove and inspect coil that did not produce a spark. Check for cranks or carbon tracking. Replace as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If coil(s) are okay, go to next step.
  18. Connect a test light across affected ICM primary terminals. Crank engine and observe test light. If test light flashes while cranking engine, go to next step. If test light does not flash, go to step 28).
  19. Check spark plug wire(s) to affected cylinders. Repair or replace as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If wire(s) are okay, go to next step.
  20. Check resistance on affected spark plug wire. Resistance should be less than 30,000 ohms. If resistance is not specified, replace spark plug wire. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If spark plug wire(s) are okay, check for poor or damaged harness connector. Check for faulty engine coolant temperature. See SYSTEM/COMPONENT TESTS article.
  21. Check cylinders No. 1, 3 and 5 spark plug wires. Replace as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If wire(s) are okay, go to next step.
  22. Check spark plug wire resistance of cylinders No. 1, 3 and 5. Resistance should be less than 30,000 ohms. If resistance is not as specified, replace wire(s). After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If wire(s) are okay, go to next step.
  23. Remove all spark plugs. If excessive fouling is found, go to step 25). If spark plugs are not fouled, go to next step.
  24. Test fuel for contamination. If fuel is contaminated, clean fuel system. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . If fuel is not contaminated, check for poor or damaged PCM connector or for faulty engine coolant temperature sensor. See SYSTEM/COMPONENT TESTS article.
  25. Check for engine mechanical problem. Check for bent push rods, faulty camshaft, leaking or sticky valves or rings, excessive valve deposits, loose or worn rocker arms, weak valve springs, incorrect valve timing or leaking head gasket. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  .
  26. Replace 7X CKP sensor. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  .
  27. Replace ignition coil(s) associated with cylinder that did not produce a spark. After repairs, perform PCM system check.
  28. Replace ignition control module. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  .
  29. Replace PCM. Perform PCM relearn procedures. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  .
Fig 1: Ignition & Injector System Circuit Schematic
G95I35806Courtesy of GENERAL MOTORS CORP.
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