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HOMESERVICE MANUALSCHEVROLET1999SUBURBAN C2500, 6.5 FREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0205-P0351DTC P0300DTC P0300: ENGINE MISFIRE DETECTED (2.2L "J" BODY & "S" SERIES)DIAGNOSTIC PROCEDURES
1999 Chevrolet Suburban C2500, 6.5 F

Diagnostic Procedures

1999 Chevrolet Suburban C2500, 6.5 FSECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
  2. If DTC P0200 is also set, diagnose that DTC before proceeding. If DTC P0200 is not set, go to next step.
  3. Perform a visual inspection of the following. Check vacuum hoses for splits, kinks and proper routing. Check for leaks at throttle body, intake manifold, EGR valve and PCV system. Check PCM grounds for proper connection. Check injector harness connectors for proper installation. Repair as necessary. After repairs, go to step  31. If no problems are found, go to next step.
  4. Start and allow engine to idle. Using scan tool, select MISFIRE DATA LIST function and monitor MISFIRE CUR. COUNTERS (one counter per cylinder). If any MISFIRE CURRENT counters are incrementing, go to next step. If any MISFIRE CURRENT counters are not incrementing, go step  6.
  5. If all counters are equal (within a percentage of each other), go to step  7. If counters are not equal (within a percentage of each other), go to step  11.
  6. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If any of MISFIRE CURRENT counters are incrementing, go to step  5. If MISFIRE CURRENT counters are not incrementing, see DIAGNOSTIC AIDS .
  7. Turn ignition off. Install fuel pressure gauge. Start engine and allow it to idle. If fuel pressure is 41-47 psi (2.9-3.3 kg/cm2 ), go to next step. If fuel pressure is not 41-47 psi (2.9-3.3 kg/cm2 ), see BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  8. Check for fuel contamination. If fuel is contaminated, go to step  10. If fuel is not contaminated, go to next step.
  9. Check for a basic engine problem (compression, cam timing, throttle body leak, restricted airflow, etc.). Repair as necessary. After repairs, go to step  31.
  10. Replace contaminated fuel. After repairs, go to step  31.
  11. Turn ignition off. Disconnect fuel injector harness connector. Temporarily remove ignition coil and Ignition Control Module (ICM) assembly. Install Spark Plug Jumper Wires (J-36012). Install Spark Tester (J-26792) to spark plug jumper for each cylinder, one at a time. Disconnect spark plug boot from companion cylinder at ignition coil housing and install a jumper wire between ground and spark plug connector at ignition coil housing (1-4 or 2-3). Crank engine and check for spark. If spark is present at all cylinders, go to next step. If spark is not present at one or more cylinders, go to step  20.
  12. Check for faulty spark plugs. Replace defective spark plug(s) as necessary. After repairs, go to step  31. If spark plugs are okay, go to next step.
  13. Turn ignition off. Disconnect fuel injector connectors from injectors. Install an injector test light on injector harness connector for cylinders that had misfired. Crank engine and note test light. If injector test light blinks, go to next step. If injector test light does not blink, go to step  15.
  14. Perform fuel injector test. See appropriate SYSTEM & COMPONENT TESTING article. If injectors are okay, go to step  9. If injectors are not okay, go to step  16.
  15. Disconnect injector test light. Using a standard test light connected to ground, probe ignition feed of injector harness connector for each affected/misfiring injector. Crank engine. If test light illuminates, go to step  17. If test light does not illuminate, go to step  19.
  16. Replace any faulty fuel injector(s). After replacing injector(s), go to step  31.
  17. Check affected fuel injector driver circuit(s) for an open, short to ground or short to voltage. If problem is found, go to next step. If circuit is okay, go to step  28.
  18. Repair as necessary. After repairs, go to step  31.
  19. Repair open ignition feed circuit between fuel injector harness connector and fuel injector. After repairs, go to step  31.
  20. Check resistance of spark plug cable on affected cylinder. If resistance is less than 30,000 ohms, go to next step. If resistance is not less than 30,000 ohms, go to step  28.
  21. Turn ignition off. Disconnect PCM harness connector. Reconnect Spark Tester (J-26792) on affected spark plug wire. Turn ignition on. Connect a fused jumper wire to battery voltage. Momentarily touch jumper to affected IC circuit at PCM harness connector. DO NOT leave jumper wire connected for longer than 5 seconds. If spark is present at spark tester when jumper is removed from IC circuit, go to step  26. If spark is not present at spark tester when jumper is removed from IC circuit, go to next step.
  22. Turn ignition off. Disconnect ICM harness connector. Check affected IC circuit for an open or short. Repair as necessary. After repairs, go to step  30. If circuit is okay, go to next step.
  23. Remove ignition coil from cylinder that did no have a spark. Check secondary coil resistance. If coil resistance is 5000-8000 ohms, go to next step. If coil resistance is not 5000-8000 ohms, go to step  29.
  24. Install a known-good ignition coil. Reconnect ICM harness connector. Connect spark tester to affected cylinder. Turn ignition on. Momentarily touch jumper wire to affected IC circuit at PCM connector. If spark is present at spark tester, go to step  30. If spark is not present at spark tester, go to next step.
  25. Check for poor connection at ICM. Repair a necessary. If connection is okay, replace ICM. After replacing ICM, go to step  30.
  26. Check for poor PCM connection. Repair as necessary. After repairs, go to step  30. If connection is okay, go to next step.
  27. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step  30.
  28. Replace spark plug cables. After replacing spark plug cables, go to step  30.
  29. Replace faulty ignition coil. After replacing ignition coil, go to next step.
  30. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function then enter DTC P0300. If scan tool indicates that test RAN AND PASSED, go to next step. If scan tool does not indicate that test RAN AND PASSED, repeat step  2.
  31. If any other DTCs are set, diagnose affected DTCs. If no other DTCs are set, system is okay.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.