Diagnostic Instructions
DTC Descriptors
DTC P0300: Engine Misfire Detected
DTC P0301: Cylinder 1 Misfire Detected
DTC P0302: Cylinder 2 Misfire Detected
DTC P0303: Cylinder 3 Misfire Detected
DTC P0304: Cylinder 4 Misfire Detected
DTC P0305: Cylinder 5 Misfire Detected
DTC P0306: Cylinder 6 Misfire Detected
Circuit/System Description
The engine control module (ECM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each
cylinder, the ECM is able to detect individual misfire events. A misfire rate that is high enough can cause 3-way catalytic converter damage. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage
are present.
Conditions for Running the DTC
• | DTCs P0016, P0102, P0103, P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, and P0340 are not set. |
• | The engine speed is less than 4,500 RPM. |
• | The engine load is less than 71 percent. |
• | The DTCs run continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value.
Action Taken When the DTC Sets
DTCs P0300, P0301, P0302, P0303, P0304, P0305 and P0306 are Type A DTCs.
Conditions for Clearing the DTC
DTCs P0300, P0301, P0302, P0303, P0304, P0305 and P0306 are Type A DTCs.
Diagnostic Aids
A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the following possible sources:
• | A tire or wheel that is out of round or out of balance |
• | Variable thickness brake rotors |
• | An unbalanced drive shaft |
• | Certain rough road conditions |
• | A damaged accessory drive component or belt |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Electronic Ignition (EI) System Description
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Engine running at the normal operating temperature. Verify there is no abnormal engine noise.
- Verify that DTC P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, or P0277 is not set.
- Clear the DTCs with a scan tool.
Important: A misfire may occur when the engine is under a load. An engine load may be necessary to verify the condition.
- Increase the engine speed to 1,500 RPM, observe the DTC information with a scan tool. DTCs P0300, P0301, P0302, P0303, P0304, P0305, or P0306 should not set.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
- Verify the following conditions do not exist:
• | Vacuum hose splits, kinks, and incorrect connections |
• | Crankcase ventilation system for vacuum leaks |
⇒ | If you find any of the above conditions, repair as necessary. |
- Ignition OFF, disconnect the ignition coil from the misfiring cylinder.
- Install the
J 26792
to the boot of the ignition coil and ground.
Important: An erratic or weak spark is considered a no spark condition.
- Attempt to start the engine. Observe the
J 26792
. The spark tester should spark.
- Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the following conditions do not exist with the spark plug:
• | Cracked, worn, incorrectly gapped |
⇒ | If there is a condition with the spark plug, replace the spark plug. |
- Exchange the suspected spark plug with another cylinder that is operating correctly.
- Engine running, disconnect the injector that corresponds to the misfiring cylinder. The engine speed should change.
⇒ | If the engine speed changes, replace the spark plug. |
- If all conditions test normal, test or inspect for the following:
Repair Instructions
Repair Verification
- If the customer concern was a flashing MIL, operate the vehicle within the conditions for running DTC P0420 or P0430. Refer to
DTC P0420 or P0430.
- Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- 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/Failure Records.
- If the DTC fails this ignition, a misfire still exists.