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Ignition System

  1. Install Tech 1 scan tool. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . Check TP sensor (stuck wide open) and Engine Coolant Temperature (ECT) sensor. ECT sensor should read close to ambient temperature. Check if all injector Diagnostic Trouble Codes (DTCs) are active. If DTC(s) are stored, diagnose DTC using TESTS W/CODES article. If injector codes are not present, go to next step.
  2. If DTC P1635 is present, diagnose DTC using TESTS W/CODES article. If DTC P1635 is not present, go to next step.
  3. If any IC related DTC is present, diagnose DTC using TESTS W/CODES article. If DTC is not present, go to next step.
  4. If any EGR related DTC is present, diagnose DTC using TESTS W/CODES article. If DTC is not present, go to next step.
  5. Using scan tool, monitor engine RPM (7X CKP reference pulse) while cranking engine. If RPM is detected, go to next step. If RPM is not detected, go to step 12).
  6. If scan tool 7X counter reads more than 100, go to step 10). If scan tool 7X counter reads 100 counts or less, check spark at cylinders No. 2 and 4.
  7. If spark is present, check for fouled spark plugs. If spark plugs are okay, go to FUEL SYSTEM test. If spark is not present, go to next step.
  8. Check ignition control module fuse or voltage to fuse with ignition on. See Fig 1 . If fuse is okay and voltage is present, go to next step. If fuse is faulty or voltage is not present, replace fuse or repair circuit.
  9. Disconnect electronic ignition control module. Turn ignition on. Using a test light, check voltage between ignition control module terminal "A" and fuse block. See Fig 1 . If voltage is present, check ignition control module terminal connector. If voltage is not present, repair open in Pink wire (circuit No. 1039) to fuse block.
  10. Check for spark on cylinders No. 2 and 4. If spark is present on both wires, go to step 12). If spark is not present on any of the spark plug wires, go to next step. If spark is present on only one wire, check spark at opposing cylinder. If spark is present at opposing cylinder, replace spark plug wire. If spark is not present at opposing cylinder, replace ignition control module.
  11. Check for proper ground to ignition control module. Check battery voltage at ignition control module terminal "A" (Pink wire). See Fig 1 . If voltage is present, check module connector. If connector is okay, module is faulty. If voltage is not present, repair open in Pink wire to control module.
  12. Turn ignition off. Disconnect PCM harness connector J3. See Fig 1 . Using DVOM, check resistance between Crankshaft Position (CKP) sensor harness connector terminals. Resistance should be 700-900 ohms. If resistance is as specified, go to next step. If resistance is not as specified, go to step 14).
  13. Set DVOM to AC scale. Connect DVOM between CKP harness connector J3 and PCM. See Fig 1 . Crank engine. DVOM should read 200 millivolts (mV). If reading is as specified, check PCM harness connector tightness. If reading is not as specified, replace CKP sensor.
  14. Check for continuity between CKP harness connector terminals. Repair as necessary. If continuity is present, check CKP sensor circuit for short to ground or voltage. Repair as necessary. If circuits are okay, go to next step.
  15. Remove CKP sensor. Check sensor resistance. Resistance should be 700-900 ohms. If resistance is not as specified, replace CKP sensor. If resistance is as specified, check if CKP sensor is still magnetized. If sensor is still magnetized, check for poor or intermittent connection at sensor harness connector.
Fig 1: Ignition System
G95D35694Courtesy of GENERAL MOTORS CORP.
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