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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1144 (Engine Controls Diagnosis - 6.0L - Alternative Fuels (DTC P0005-DTC P2665)) >> Diagnosis >> DTC P0300-P0308: Engine Misfire Detected >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 5:  This step determines if the engine is misfiring while operating on the gasoline fuel system.
  2. 7:  If the Misfire Current Counters are incrementing, but the engine is NOT misfiring, this indicates a mechanical condition. For example, an accessory drive belt could cause this condition.
  3. 8:  This step verifies that the Crankshaft Variation Learn Procedure is performed. A crankshaft variation that is not learned may cause the misfire counters to increment.
  4. 10:  The spark should be consistent when you test the spark at the spark plug wires. The presence of few sparks then nothing indicates no spark.
  5. 14:  A misfiring cylinder may cause more than one misfire counter to increment. Diagnose the fuel injector circuit of the cylinder that displays the highest level of misfire.
  6. 20:  A severe misfire can damage the catalytic converter. This step verifies that the catalytic convertors are operating correctly.
DTC P0300 - Engine Misfire Detected

Step Action Values Yes No
1 Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Alternative Fuels (Engine Controls)
2
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the DTC information with a scan tool.
Are there any other DTCs set?		 - Go to Diagnostic Trouble Code (DTC) List Go to Step 3 
3
  1. Start the engine.
  2. Clear the DTCs with a scan tool.
  3. Allow the engine to reach operating temperature.
  4. Observe the Misfire Current Counters with a scan tool.
Are any of the Misfire Current Counters incrementing?		 - Go to Step 7  Go to Step 4 
4 Is the vehicle equipped with the bi-fuel option (KL6)? - Go to Step 5  Go to Step 6 
5 
  1. Force a switch over to gasoline with the scan tool output controls function.
  2. Observe the Misfire Current Counters with a scan tool.
Are any of the Misfire Current Counters incrementing?		 - Go to DTC P0200  Go to Step 6 
6
  1. Observe the Freeze Frame and the Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame, and the Failure Records data.
Does the DTC fail this ignition cycle?		 - Go to Step 7  Go to Diagnostic Aids
7  Is the engine misfiring? - Go to Step 9  Go to Step 8 
8 
  1. Perform the Crankshaft Variation Learn Procedure. Refer to CKP System Variation Learn Procedure in Engine Controls in the C/K Pickup Service Manual.
  2. Start the engine.
  3. Observe the Misfire Current Counters with a scan tool.
Are any of the Misfire Current Counters incrementing?		 - Go to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual Go to Step 21 
9 Observe the Misfire Current Counters with a scan tool.
Is there only one Misfire Current Counter incrementing?		 - Go to Step 10  Go to Step 16 
10 
  1. Turn OFF the ignition.
  2. Disconnect the spark plug wire from the spark plug that indicates a misfire. Refer to Spark Plug Wire Replacement in Engine Controls in the C/K Pickup Service Manual.
  3. Connect the J 26792 Spark Tester to the spark plug wire and a good ground.
  4. Start and idle the engine.
Does the spark tester spark and is the spark consistent?		 - Go to Step 12  Go to Step 11 
11
  1. Turn OFF the ignition.
  2. Remove the spark plug wire from the cylinder that indicates a misfire. Refer to Spark Plug Wire Replacement in Engine Controls in the C/K Pickup Service Manual.
  3. Measure the resistance of the spark plug wire with a DMM.
Is the resistance less than the specified value?		 625 Ω Per 30 cm (Per Foot) Go to Electronic Ignition (EI) System Diagnosis in Engine Controls in the C/K Pickup Service Manual Go to Step 18 
12
  1. Remove the spark plug from the cylinder that indicates a misfire. Refer to Spark Plug Replacement in Engine Controls in the C/K Pickup Service Manual.
    2. IMPORTANT: If the spark plug is gas, coolant, or oil fouled, determine the cause of the fouling. Refer to DTC P0172 or P0175 in Engine Controls in the C/K Pickup Service Manual for spark plugs that are gasoline fouled. Refer to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual for spark plugs that are coolant or oil fouled.
  2. Inspect the spark plug. Refer to Spark Plug Inspection in Engine Controls in the C/K Pickup Service Manual.
Did you find and correct the condition?		 - Go to Step 19  Go to Step 13 
13
  1. Swap the suspected spark plug with another cylinder that is operating correctly.
  2. Start the engine.
  3. Operate the engine within the conditions that the misfire occurred.
  4. Monitor the Misfire Current Counters with a scan tool.
Did the misfire move with the spark plug?		 - Go to Step 17  Go to Step 14 
14 
IMPORTANT:
  • Make sure all the injectors operate. High resistance in an injector circuit causes the injector to be inoperative without setting a fuel injector DTC.
  • Return to this diagnostic after you complete the Fuel Injector Coil Test.
Perform the Fuel Injector Coil Test. Refer to Fuel Injector Coil Test .Did you find and correct the condition?		 - Go to Step 19  Go to Step 15 
15 Perform the Fuel System Diagnosis. Refer to Fuel System Diagnosis .
Did you find and correct the condition?		 - Go to Step 19  Go to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual
16 Inspect or test for the following conditions:
  • Inspect the vacuum hoses for splits, kinks, and the correct connections.
  • Inspect for vacuum leaks at the throttle body and at the intake manifold.
  • Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the correct location.
  • Test for the correct fuel pressure. Refer to Fuel System Diagnosis .
  • Inspect for faulty spark plug wires. Refer to Spark Plug Wire Inspection in Engine Controls in the C/K Pickup Service Manual.
  • Inspect for fouled or damaged spark plugs. Refer to Spark Plug Inspection in Engine Controls in the C/K Pickup Service Manual.
  • Inspect the exhaust system for restrictions. Refer to Restricted Exhaust in Engine Exhaust in the C/K Pickup Service Manual.

Did you find and correct the condition?		 - Go to Step 19  Go to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual
17 Replace the spark plug. Refer to Spark Plug Replacement in Engine Controls in the C/K Pickup Service Manual.
Did you complete the replacement?		 - Go to Step 19  -
18 Replace the spark plug wire. Refer to Spark Plug Wire Replacement in Engine Controls in the C/K Pickup Service Manual.
Did you complete the replacement?		 - Go to Step 19  -
19 Was the customers concern that the was malfunction indicator lamp (MIL) flashing? - Go to Step 20  Go to Step 21 
20 
  1. Operate the vehicle at the specified value for 4 minutes.
  2. Operate the vehicle within the Conditions for Running the DTC P0420 or P0430 as specified in the supporting text. Refer to DTC P0420 or P0430 (Without HP2) DTC P0420 or P0430 (With HP2) .
Does the DTC run and pass?		 2,500 RPM Go to Step 21  Go to DTC P0420 or P0430 (Without HP2) DTC P0420 or P0430 (With HP2) in Engine Controls in the C/K Pickup Service Manual
21
  1. Use the scan tool in order to clear the DTCs.
  2. Turn the ignition OFF for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC.
Does the DTC run and pass?		 - Go to Step 22  Go to Step 2 
22 With a scan tool, select Capture Info in order to observe the stored information.
Does the scan tool display any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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