Excerpt from SI.
Important

Remove any debris from the PCM connector surfaces before servicing the
PCM. Inspect the PCM connector gaskets when diagnosing/replacing the
PCM. Ensure that the gaskets are installed correctly. The gaskets
prevent water intrusion into the PCM.

    * Running the vehicle out of fuel causes sufficient misfire to set
DTC P0300. A vehicle that is out of fuel may have fuel level DTCs also set.
    * A restricted fuel filter can cause sufficient misfire to set DTC
P0300. Refer to Fuel System Diagnosis .
    * Excessive vibration from sources other than the engine could
cause a misfire DTC. The following are possible sources of vibration:
          o Variable thickness brake rotor
          o Drive shaft not balanced
          o Certain rough road conditions
    * Observe, if more then one cylinder is mis-firing, the scan tool
may only display one cylinder mis-firing. This will not be apparent
until the repair is completed. Also, if an ignition coil/module ground
circuit is open for one side of the engine, the scan tool may only
display 2 or 3 cylinders mis-firing. Inspect the ground circuit for the
ignition coil/modules on the cylinder bank of the engine that has more
then one cylinder mis-firing.

Test Description

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

   2.

      Wetting down the secondary ignition system with water from a
spray bottle may help locate damaged or deteriorated components.
Look/listen for arcing or misfiring as you apply the water.

      If the Misfire Current counters are incrementing and there is no
apparent misfire, an erratic CKP sensor signal could be the cause.
Perform the diagnostic table for DTC P0335 first if this condition is
suspected.

      If a misfire is present and you suspect a fuel control problem,
force the fuel system into Open Loop using the scan tool and allow the
engine to run for a few minutes. If this eliminates the misfire, refer
to any fuel control related DTCs which are set. If no other DTCs are
set, refer to the Engine Scan Tool Data List.

      A misfire may not be apparent at idle. The misfire may only occur
above idle under a load. Road test the vehicle and monitor the misfire
current counters.

      If more than one cylinder is misfiring, the misfire current
counters may only increment for only one cylinder. Example: Cylinders 1
and 8 are both misfiring, yet only cylinder 8 increments on the misfire
current counter.

      If one of the injector fuses is open, only two or three misfire
current counters may increment for the corresponding side of the engine.
   4.

      The cylinder with the more significant misfire may cause another
cylinders counter to increment only by a small amount.
  10.

      If the engine misfire moves with the spark plug, this is good
indication that you should replace the spark plug.
  12.

      If there are no fuel system problems, refer to
      Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L,
6.0L. An engine mechanical problem can cause a spark plug to gas foul.
Inspect for loose rockers, collapsed lifters or worn camshaft lobes.

  17.

      If the customers concern is the MIL is flashing, this indicates
that a Catalyst Misfire has occurred. Drive the vehicle in the
conditions to run the catalyst diagnostic. Refer to
      DTC P0420 Catalyst System Low Efficiency Bank 1 and/or DTC P0430
Catalyst System Low Efficiency Bank 2 .

DTC P0300 - Engine Misfire Detected

Step
   

Action
   

Value(s)
   

Yes
   

No

1
   

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?
   

--
   

Go to Step 2
   

Go to Powertrain On Board Diagnostic (OBD) System Check

2

   

Important

    * You must perform the CKP System Variation Learn Procedure before
proceeding with this diagnostic table. Refer to CKP System Variation
Learn Procedure .
    * If any DTCs are set, refer to those DTCs before proceeding with
this diagnostic.
    * If any abnormal engine mechanical noise can be heard refer to
Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.

   1. Install the scan tool.
   2. Idle the engine.
   3. Monitor all the Misfire Current counters on the misfire data list
(There are a total of 8 counters, One counter per cylinder) using the
scan tool.

Are any of the Misfire Current counters incrementing?
   

--
   

Go to Step 4
   

Go to Step 3

3
   

   1. Turn ON the ignition leaving the engine OFF.
   2. Review the Freeze Frame and/or Failure Records data for this DTC
and observe the parameters.
   3. Turn OFF the ignition for 15 seconds.
   4. Start the engine.
   5. Operate the vehicle within the conditions required for this
diagnostic to run, and as close to the conditions recorded in Freeze
Frame/Failure Records as possible. Special operating conditions that you
need to meet before the PCM will run this diagnostic, where applicable,
are listed in Conditions for Running the DTC.
   6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC
option, and then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?
   

--
   

Go to Step 4
   

Go to Diagnostic Aids

4

   

Is only one Misfire counter incrementing?
   

--
   

Go to Step 6
   

Go to Step 5

5
   

Visually/physically inspect the following items:

    * Accessory drive belt and pulleys for damage or misalignment.
Refer to Drive Belt Chirping Diagnosis in Engine Mechanical 4.8L, 5.3L,
6.0L.
    * Vacuum hoses for splits, kinks and proper connections. Refer to
Emission Hose Routing Diagram .
    * Throttle body and intake manifold for vacuum leaks
    * Crankcase ventilation valve and/or system for vacuum leaks. Refer
to Crankcase Ventilation System Description .
    * PCM grounds for being clean and secure. Refer to Ground
Distribution Schematics in Wiring Systems.
    * Inspect the Ignition Coil/Module ground circuit for an open on
the side of the engine that has more than one cylinder mis-firing. An
open ground causes all four Ignition Coil/Module to be inoperative. The
Mis-fire current counters only displays 2-3 cylinders mis-firing, not
all four cylinders.
    * Inspect that all injector harness connectors are connected to the
proper injector/cylinder
    * Check the injector and Ignition Control fuses for being open. If
you find an open fuse, locate and repair the shorted circuit. Refer to
Wiring Repairs in Wiring Systems.
    * Test for incorrect fuel pressure or restricted fuel flow. Refer
to Fuel System Diagnosis .
    * Inspect for a restricted exhaust. Refer to Restricted Exhaust
System Check .
    * Test for fuel contamination. Refer to
Alcohol/Contaminants-in-Fuel Diagnosis .
    * If an abnormal engine mechanical noise is heard, refer to Base
Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.

Did any of the above checks isolate a condition requiring a repair?
   

--
   

Go to Step 17
   

Go to Step 6

6
   

Important

Before disconnecting the injector harness refer to Fuel Rail Assembly
Replacement . There is a special procedure for disconnecting the fuel
injector harness connectors.

   1. Turn OFF the ignition.
   2. Disconnect the injector that corresponds to the Misfire Current
counter(s) that was incrementing.
   3. Connect the injector test lamp J 34730-405 to the injector
electrical connector.
   4. Idle the engine.

Is the injector test lamp flashing?
   

--
   

Go to Step 7
   

Go to DTC P0200 Injector Control Circuit

7
   

   1. Turn OFF the ignition.
   2. Reconnect the injector harness electrical connector.
   3. Disconnect the ignition wire(s) from the spark plug that
corresponds to the Misfire Current counter(s) that was incrementing.
Refer to Spark Plug Wire Harness Replacement in Engine Electrical.
   4. Install the spark tester J 26792 to a ground.
   5. Start the engine.

Does the spark jump the tester gap and is the spark consistent?
   

--
   

Go to Step 9
   

Go to Step 8

8
   

   1. Remove the ignition wire for the cylinder that is Mis-firing.
Refer to Spark Plug Wire Harness Replacement in Engine Electrical.
   2. Measure the resistance of the ignition wire using the DMM J 39200 .

Is the ignition wire resistance less than the specified resistance?
   

700ohms
   

Go to Electronic Ignition (EI) System Diagnosis
   

Go to Step 16

9
   

Remove the spark plug(s) from the cylinder that indicated a misfire.
Refer to Spark Plug Replacement in Engine Electrical.

Does the spark plug appear to be OK?
   

--
   

Go to Step 10
   

Go to Step 11

10

   

Important

If the Injector Coil Test Procedure checks to be OK, refer to Base
Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.

   1. Swap the suspected spark plug with another cylinder that is
operating properly. Refer to Spark Plug Replacement in Engine Electrical.
   2. Operate the vehicle under the same conditions that the misfire
occurred.

Did the misfire move with the spark plug?
   

--
   

Go to Step 15
   

Go to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Between
10-35 Degrees C (50-95 Degrees F)

11
   

Are the spark plugs oil or coolant fouled.
   

--
   

Go to Base Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.
   

Go to Step 12

12

   

Important

If the Fuel System checks to be OK, refer to Base Engine Misfire
Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.

Are the spark plugs gas fouled?
   

--
   

Go to Fuel System Diagnosis
   

Go to Step 13

13
   

Important

If the Injector Coil Test Procedure checks to be OK, refer to Base
Engine Misfire Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.

Do the spark plugs show any signs of being cracked, worn, or improperly
gapped?
   

--
   

Go to Step 14
   

Go to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside
10-35 Degrees C (50-95 Degrees F)

14
   

Replace or re-gap spark plugs. Refer to Spark Plug Replacement in Engine
Electrical. If an improper gap is found, be sure to re-gap spark plugs
using a wire type gauge.

Is the action complete?
   

--
   

Go to Step 17
   

--

15
   

Replace the faulty spark plug(s). Refer to Spark Plug Replacement in
Engine Electrical.

Is the action complete?
   

--
   

Go to Step 17
   

--

16
   

Replace the faulty ignition wire(s). Refer to Spark Plug Wire Harness
Replacement in Engine Electrical.

Is the action complete?
   

--
   

Go to Step 17
   

--

17

   

Was the customers concern that the MIL was flashing?
   

--
   

Go to DTC P0420 Catalyst System Low Efficiency Bank 1 or DTC P0430
Catalyst System Low Efficiency Bank 2 .
   

Go to Step 18

18
   

   1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC
Information option using the scan tool.
   2. Idle the engine at the normal operating temperature.
   3. Select the Diagnostic Trouble Code (DTC) option and the Specific
DTC option, then enter the DTC number using the scan tool.
   4. Operate the vehicle within the Conditions for Running the DTC as
specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?
   

--
   

Go to Step 19
   

Go to Step 2

19
   

Select the Capture Info option and the Review Info option using the scan
tool.

Does the scan tool display any DTCs that you have not diagnosed?
   

--
   

Go to the applicable DTC table
   

System OK