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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 258 (Engine Controls Self-Diagnostics - 2.2L) >> Diagnostic Tests >> DTC P0300: Engine Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 GMC Sonoma and 2003 Chevrolet S10 Pickup. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
    2. NOTE: You must perform the Crankshaft Position (CKP) system variation learn procedure before proceeding with this diagnostic test. Refer to CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE  .
  2. Start engine. Allow engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records. Monitor all of the Misfire Current counters with scan tool. Are any of the Misfire Current counters incrementing? If yes, go to next step. If no, see DIAGNOSTIC AIDS  .
  3. Are any other DTCs set? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, go to next step.
  4. Can any abnormal engine noise be heard? If yes, diagnose for engine mechanical problem. If no, go to next step.
  5. Observe the Misfire History Cyl# parameter with a scan tool. Does more than one cylinder indicate a large count value for the Misfire History Cyl# parameter? If yes, go to next step. If no, go to step  8 .
  6. Are the Misfire History Cyl# counts indicated for companion cylinders 1/4 or 2/5 or 3/6? If yes, go to step  8 . If no, go to next step.
  7. Inspect vacuum hoses and seals for splits, kinks, and proper connection. Check throttle body and intake manifold for vacuum leaks and crankcase ventilation system for vacuum leaks. Check for clean and secure PCM grounds. Check for restricted exhaust. Check for fuel contamination. Did you find and correct the condition? If yes, go to step  20 . If no, go to next step.
  8. Turn ignition off. Disconnect spark plug wire from the spark plug that corresponds to the Misfire Current counters that were incrementing. Install Spark Tester (J-26792) to a good ground. Jumper the spark plug end of the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil. Start engine. Does the spark jump the tester gap and is the spark consistent? If yes, go to step  10 . If no, go to next step.
  9. Remove spark plug wire for the affected cylinder. Inspect spark plug wire. Measure resistance of the spark plug wire with a DVOM. Is spark plug wire resistance less than 700 ohms? If yes, diagnose electronic ignition system. See ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 2.2L SONOMA & S10 PICKUP article. If no, go to step  19 .
  10. Remove spark plug from cylinder that indicated a misfire. Inspect spark plug. Does the spark plug appear to be okay? If yes, go to next step. If no, go to step  12 .
  11. Exchange the suspected spark plug with another cylinder that is operating properly. Operate the vehicle under the same conditions that the misfire occurred. Did the misfire move with the spark plug? If yes, go to step  18 . If no, go to step  15 .
  12. Is spark plug oil or coolant fouled? If yes, diagnose for an engine mechanical problem. Repair as necessary. After repairs, go to next step.
  13. Is spark plug gas fouled? If yes, go to step  16 . If no, go to next step.
  14. Does the spark plug show any signs of being cracked, worn or improperly gapped? If yes, go to step  17 . If no, go to next step.
  15. Perform the fuel injector coil test. Refer to FUEL INJECTOR COIL TEST under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 2.2L SONOMA & S10 PICKUP article. If no, diagnose for an engine mechanical problem.
  16. Diagnose fuel system. Did you find and correct the condition? If yes, go to step  20 . If no, diagnose for an engine mechanical problem.
  17. Replace or gap spark plug. After regapping or replacing spark plug, go to step  20 .
  18. Replace faulty spark plug. After replacing spark plug, go to step  20 .
  19. Replace faulty spark plug wires. After replacing spark plug wires, go to next step.
  20. Was the customer's concern regarding the MIL flashing? If yes, go to next step. If no, go to step  22 .
  21. Operate engine at 2500 RPM for 4 minutes. If the customer's concern regarding the MIL flashing? Operate the vehicle within the Conditions for Running. See CONDITIONS FOR RUNNING DTC  . Does the DTC run and pass? If yes, go to next step. If no, go to DTC P0420: TWC SYSTEM - LOW EFFICIENCY  .
  22. Use the scan tool in order to clear the DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC  . Does the DTC run and pass? If yes, go to next step. If no, go to step  2 .
  23. With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, system is okay.
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