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
Circuit/System Description
The engine control module (ECM) uses information from the crankshaft position (CKP) sensor in order to determine when an engine misfire is occurring and uses information from the camshaft position (CMP) sensor in order to determine which cylinder is misfiring.
By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM is able to detect individual misfire events. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 sets. Under
certain driving conditions, a misfire rate can be high enough to cause the 3-way catalytic converter (TWC) to overheat, possibly damaging the converter. The malfunction indicator lamp (MIL) will flash ON and OFF when converter overheating, damaging conditions
are present and DTC P0300 is set. DTCs P0301-P0304 correspond to cylinders 1-4. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set.
Conditions for Running the DTC
• | DTCs P0121, P0122, P0123, P0221, P0222, P0335, or P0336 are not set. |
• | The engine speed is between 400-6,285 RPM. |
• | The engine coolant temperature (ECT) is greater than -30°C (-22°F). |
• | The fuel level is more than 12 percent. |
• | The ECM is not in fuel shut-off or decel fuel cut-off mode. |
• | DTCs P0300, and P0301-P0304 run continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission or catalytic converter damaging levels to exceed mandated standards.
Action Taken When the DTC Sets
DTCs P0300-P0304 are Type B DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0300-P0304 are Type B DTCs.
Diagnostic Aids
• | A misfire may only occur when the engine is under a load or when the engine is cold. |
• | 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 |
- | A damaged reluctor wheel |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Special Tools
J 26792 (SA91992) HEI Spark Tester
Circuit/System Verification
- Verify that no other DTCs are set.
- Engine idling, verify there is no abnormal engine noise.
- Observe the Misfire Current Counters with a scan tool. The Misfire Current Counters should not be incrementing. Random misfires that are not steadily incrementing may be normal.
- If the vehicle passes the Circuit/System Verification test, operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.
Circuit/System Testing
- Verify that the following conditions do not exist:
⇒ | If you find any of the above conditions, repair as necessary. |
- Ignition OFF, remove the ignition coil from the misfiring cylinder, leaving the electrical connector connected.
- Install the
J 26792 (SA91992) Spark Tester
to the boot of an ignition coil and ground.
Note: An erratic or weak spark is considered a no spark condition.
- Attempt to start the engine and observe the
J 26792 (SA91992) Spark Tester
. 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:
• | Gas, coolant, or oil fouled |
⇒ | 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.
- Operate the engine under the conditions in which the misfire occurred. Observe the Misfire Current Counters with a scan tool. The misfire should not follow the spark plug exchange.
⇒ | If the misfire follows the spark plug, replace the spark plug. |
- If all conditions test normal, test or inspect for the following:
Repair Instructions
Repair Verification
- Install any components or connectors that have been removed or replaced during diagnosis.
- Perform any adjustment, programming or setup procedures that are required when a component or module is removed or replaced.
- Clear the DTCs.
- Turn OFF the ignition for 60 seconds.
- If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the
Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
- To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to
DTC P0420.