P0300

P0300-MULTIPLE CYLINDER MISFIRE

For a complete wiring diagram refer to the Wiring Information Electrical Diagrams.

Theory of Operation

The Misfire Monitor gathers and filters engine crank speed data for 10 seconds once the monitor conditions are met. If the crank speed deviation for a cylinder is less than a calibrated value, a misfire fault is set for that cylinder. If more than one cylinder is failed, a multiple cylinder misfire fault is set. The ECM illuminates the MIL lamp after the diagnostic runs and fails twice. During this time the customer may experience a cylinder miss or engine stumble. The ECM will turn off the MIL lamp once the diagnostic runs and passes in 4 consecutive drive cycles.

- When Monitored:
While the engine is idling.

- Set Condition:
Misfire detected on multiple cylinders.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure

1. LOW FUEL
1. Using the scan tool, verify that the fuel level is above 15%.

Is the fuel level above 15%?

Yes

- Go To 2

No

- Add fuel, Go To 2
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

2. OTHER DTC'S
1. Read the Freeze frame data.

Is the DTC equal to the freeze frame DTC?

Yes

- Go To 3

No

- Repair any other DTC's first.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

3. DAMAGED FUEL LINES
1. Visually inspect the injector supply lines for damage.

Do you have any kinked or bent fuel lines?

Yes

- Repair or replace damaged fuel lines.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

No

- Go To 4

4. VALVE TRAIN
1. Visually inspect the valve train and check the valve lash on the suspect cylinders.

Is the valve train functional and the lash within the specifications listed in the service manual?

Yes

- Go To 5

No

- Adjust the lash or fix or repair any damaged components.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

5. OBSTRUCTED FUEL INJECTOR SUPPLY
1. Remove the fuel injector supply lines for the suspect cylinders.
2. Inspect both ends of the fuel injector supply lines for damage.
3. Using shop air pressure, blow out the fuel injector supply lines to verify that they are not obstructed.

Are the fuel lines free of debris or damage?

Yes

- Go To 6

No

- Replace the damaged or obstructed fuel injector supply lines.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

6. DAMAGED OR OBSTRUCTED HIGH PRESSURE CONNECTORS
1. Remove the high pressure connectors for the suspect cylinders.
2. Inspect both ends of the high pressure connectors for signs of damage.
3. Using shop air pressure, blow out the high pressure connectors to verify that they are not obstructed.

Are the high pressure connectors free of debris or damage?

Yes

- Go To 7

No

- Replace the damaged or obstructed high pressure connectors.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

7. FUEL INJECTORS
1. Remove the suspect fuel injectors.

Are the fuel injectors damaged?

Yes

- Replace the external damaged fuel injectors AND high pressure connectors.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

No

- Go To 8

8. INTERNAL DAMAGED FUEL INJECTOR
1. With the scan tool, erase DTCs.
2. Switch the misfiring injectors AND high pressure connectors with injectors AND high pressure connectors from cylinders that are firing properly.
3. Operate the vehicle.

Did the misfire DTC follow the suspect injectors AND high pressure connectors?

Yes

- Replace the internal damaged fuel injector and high pressure connector.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

No

- Go To 9

9. INTERNAL ENGINE DAMAGE
1. Perform Engine Compression Test Component Tests and General Diagnostics.

Did the suspect cylinders pass the compression test?

Yes

- Go To 10

No

- Repair the internal damage to the engine.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test

10. INTERNAL ENGINE DAMAGE
1. Perform engine leak down test Component Tests and General Diagnostics.

Did the suspect cylinders pass the leak down test?

Yes

- Test Complete.

No

- Repair the internal damage to the engine.
- Perform POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test