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Ignition System

  1. Install scan tool. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in TESTS W/CODES article. Check TP sensor (stuck wide open) and Engine Coolant Temperature (ECT) sensor. ECT sensor should read close to ambient temperature. Check if injector Diagnostic Trouble Codes (DTCs) are stored. If injector DTC(s) is present, diagnose DTC(s). See TESTS W/CODES article. If injector DTC(s) is not present, go to next step.
  2. If DTC P1635 is present, diagnose DTC. See TESTS W/CODES article. If DTC P1635 is not present, go to next step.
  3. If any IC related DTC is present, diagnose DTC. See TESTS W/CODES article. If DTC is not present, go to next step.
  4. If an EGR related DTC is present, diagnose DTC. See TESTS W/CODES article. If EGR 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, check spark at cylinders No. 2 and 4. If scan tool 7X counter reads 100 counts or less, go to step 10).
  7. If spark is present, check for fouled spark plugs. If spark plugs are okay, go to FUEL SYSTEM  . If spark is not present, go to next step.
  8. Check Electronic Ignition (EI) system 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 (EI) module. Turn ignition on. Using a test light, check voltage between EI module terminal "A" and fuse block. See Fig 1 . If voltage is present, check EI module connector tightness. If connector is okay, EI module is faulty. If voltage is not present, repair open in Pink wire (circuit No. 1039) between EI module and fuse block.
  10. Check for spark on cylinders No. 2 and 4. If spark is present on both wires, go to FUEL SYSTEM  . 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 EI module.
  11. Check for proper ground to EI module. Check battery voltage at EI module terminal "A" (Pink wire). See Fig 1 . If voltage is present, check EI module connector tightness. If connector is okay, EI module is faulty. If voltage is not present, repair open in Pink wire (circuit No. 1039) between EI module and fuse block.
  12. Turn ignition off. Disconnect PCM connector J3. See Fig 1 . Using DVOM, check resistance between PCM connector J3, terminals D13 (7X ref hi circuit) and D14 (7X ref lo circuit). 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 PCM connector J3, terminals D13 (7X ref hi circuit) and D14 (7X ref lo circuit). See Fig 1 . Crank engine. DVOM should read 200 millivolts. If reading is as specified, check PCM connector tightness. If reading is not as specified, replace Crankshaft Position (CKP) sensor.
  14. Check for continuity of 7X ref hi circuit (Yellow wire) and 7X ref lo circuit (Purple wire). See Fig 1 . Repair as necessary. If continuity is present, check circuits for short to ground or voltage. Repair as necessary. If circuits are okay, go to next step.
  15. Remove CKP sensor. Check CKP sensor resistance. Resistance should be 700-900 ohms. If resistance is not as specified, replace CKP sensor. If resistance is as specified, go to next step.
  16. Check if CKP sensor is still magnetized. If sensor is not still magnetized, replace CKP sensor. If sensor is still magnetized, check for poor or intermittent connection at sensor connector.
Fig 1: Ignition System
G95D35694Courtesy of GENERAL MOTORS CORP.
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