P0300
P0300-MULTIPLE CYLINDER MISFIREWHEN MONITORED
While the engine is idling.
SET CONDITION
Misfire detected on multiple cylinders.
POSSIBLE CAUSES
- Low fuel
- Other DTC's
- Damaged fuel lines
- Valve train
- Obstructed fuel injector supply lines
- Damaged or obstructed high pressure connectors
- External damaged fuel injectors
- Internal damaged fuel injector
- No compression
- Excessive engine leak down
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. LOW FUEL
Using the scan tool, verify that the fuel level is above 15%.
Q: Is the fuel level above 15%?
YES: Go To 2
NO: Add fuel go to step 2. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
2. OTHER DTC'S
Read the Freeze frame data.
Q: Is the DTC equal to the freeze frame DTC?
YES: Go To 3
NO: Repair any other DTC's first. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
3. DAMAGED FUEL LINES
Visually inspect the injector supply lines for damage.
Q: Do you have any kinked or bent fuel lines?
YES: Repair or replace damaged fuel lines. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 4
4. VALVE TRAIN
Visually inspect the valve train and check the valve lash on the suspect cylinders.
Q: Is the valve train functional and the lash within the specifications?
YES: Go To 5
NO: Adjust the lash or fix or repair any damaged component(s). Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
5. OBSTRUCTED FUEL INJECTOR SUPPLY
Remove the fuel injector supply lines for the suspect cylinders.
Inspect both ends of the fuel injector supply lines for damage.
Using shop air pressure, blow out the fuel injector supply lines to verify that they are not obstructed.
Q: Are the fuel lines free of debris or damage?
YES: Go To 6
NO: Replace the damaged or obstructed fuel injector supply lines. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
6. DAMAGED OR OBSTRUCTED HIGH PRESSURE CONNECTORS
Remove the high pressure connectors for the suspect cylinders.
Inspect both ends of the high pressure connectors for signs of damage.
Using shop air pressure, blow out the high pressure connectors to verify that they are not obstructed.
Q: Are the high pressure connectors free of debris or damage?
YES: Go To 7
NO: Replace the damaged or obstructed high pressure connectors. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
7. FUEL INJECTORS
Remove the suspect fuel injectors.
Q: Are the fuel injectors damaged?
YES: Replace the external damaged fuel injectors & high pressure connectors. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 8
8. INTERNAL DAMAGED FUEL INJECTOR
With the scan tool, erase DTCs.
Switch the misfiring injectors & high pressure connectors with injectors & high pressure connectors from cylinders that are firing properly.
Operate the vehicle.
Q: Did the misfire DTC follow the suspect injectors & high pressure connectors?
YES: Replace the internal damaged fuel injector and high pressure connector. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 9
9. INTERNAL ENGINE DAMAGE
Perform engine compression test
Q: Did the suspect cylinders pass the compression test?
YES: Go To 10
NO: Repair the internal damage to the engine. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
10. INTERNAL ENGINE DAMAGE
Perform engine leak down test
Q: Did the suspect cylinders pass the leak down test?
YES: Test Complete.
NO: Repair the internal damage to the engine. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1