P0300
DTC P0300-P0308
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructionsprovides an overview of each diagnostic category.
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
DTC P0307
- Cylinder 7 Misfire Detected
DTC P0308
- Cylinder 8 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 catalytic converter to overheat, possibly damaging the converter. The malfunction indicator lamp (MIL) will flash ON and OFF when catalytic converter overheating conditions are present and DTC P0300 is set. DTCs P0301-P0308 corresponds to cylinders 1-8. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will also set.
Conditions for Running the DTC
* DTCs P0016, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0220, P0222, P0223, P0335, P0336, P0606, P0641, P0651, P1516, P2101, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, and P2176 are not set.
* DTCs P0010 and P0011 are not set - without LU3.
* When DTC P0315 is set, the engine speed must be greater than 1,000 RPM.
* Engine run time is greater than 2 crankshaft revolutions.
* The engine speed is between 375-5,600 RPM.
* The ignition voltage is between 9-32 V.
* The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F).
* When the startup ECT is colder than -7°C (+19°F), this diagnostic will be delayed until the ECT is warmer than +21°C (+69°F).
* The fuel level is greater than 10 percent.
* The ECM is not in fuel shut-off, or decel fuel cut-off mode.
* The electronic brake control module (EBCM) and the traction control system (TCS) are not active or detecting rough road.
* An automatic transmission shift with a throttle position greater than 95 percent is not occurring.
* The power management is not active.
* Excessive drive wheel slip is not detected.
* The power take-off (PTO) is disabled, where applicable.
* The cylinder deactivation is not in progress, where applicable.
* DTCs P0300-P0308 run continuously when the above conditions are met.
Conditions for Setting the DTC
DTC P0300
The ECM is detecting a crankshaft speed change indicating a random misfire is occurring that exceeds mandated emission level standards or is at catalytic converter damaging levels.
DTC P0301, P0302, P0303, P0304, P0305, P0306, P0307, or P0308
The ECM is detecting a crankshaft speed change indicating a single cylinder misfire is occurring that exceeds mandated emission level standards or is at catalytic converter damaging levels.
Action Taken When the DTC Sets
* DTCs P0300-P0308 are Type B DTCs.
* When the MIL is flashing the fuel injector may be disabled for the misfiring cylinder to protect the catalytic converter.
* Depending on the conditions that set the DTC, the engine may go into Open Loop.
Conditions for Clearing the MIL/DTC
DTCs P0300-P0308 are Type B DTCs.
Diagnostic Aids
* The Crankshaft Position System Variation Learn procedure may need to be performed. Refer to Crankshaft Position System Variation Learn Testing and Inspection
* Ensure that each fuel injector is connected to the proper fuel injector harness connector. Refer to Engine Controls Schematics [1][2]Electrical Diagrams
* A high resistance condition on any fuel injector control circuit can cause an engine misfire P0300-P0308 DTC to set without setting a fuel injector circuit P0201-P0208 DTC.
* A high resistance condition on any ignition control (IC) circuit can cause an engine misfire P0300-P0308 DTC to set without setting an IC circuit P0351-P0358 DTC.
* A misfire may only occur when the engine is operating 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 the following for possible sources of vibration:
- A tire or wheel that is out of round or balance
- Variable thickness brake rotors
- An unbalanced drive shaft
- Certain rough road conditions
- A damaged accessory drive component or belt; remove the belt and safely operate the engine to evaluate
- A damaged reluctor wheel
Reference Information
Schematic Reference
Engine Controls Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Connector End Views By Name
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
* Powertrain Component Views Top of Engine Components (except LZ1)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Programming and Relearning for scan tool information
Special Tools
* J 26792 HEI Spark Tester
* For equivalent regional tools, refer to Special Tools Tools and Equipment.
Circuit/System Verification
1. Engine idling, verify there is no abnormal engine noise.
• If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical.
2. Observe the DTC information with a scan tool. Verify that DTC P0201-P0208, P0315, P0335, P0336, P0351-P0358 are not set.
• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
Note:
* A misfire may only occur when the engine is under load. An engine load may be necessary to verify the condition.
* Random misfires that are not steadily incrementing may be normal.
3. Engine idling, observe the Misfire Current Cyl. 1-8 Counter parameters with a scan tool. The misfire current counter parameters should not be incrementing.
4. Operate the vehicle within the Conditions for Running the DTC to verify that 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
Note: You must perform the Circuit/System Verification first.
1. Verify that the following conditions do not exist:
* The fuel injector wire harness electrical connectors are connected to the wrong fuel injectors. Refer to Engine Controls Schematics [1][2]Electrical Diagrams.
* Engine vacuum leaks
* Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis .
* Contaminated fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
* Restricted exhaust system-Refer to Restricted Exhaust Restricted Exhaust.
• If you find any of the above conditions, repair as necessary.
2. Ignition OFF, install the J 26792 to the spark plug wire boot of the misfiring cylinder.
Note: An erratic or weak spark is considered a no spark condition.
3. Attempt to start the engine and observe the J 26792 . The spark tester should spark.
• If there is no spark, test the spark plug wire for the correct resistance, refer to Ignition System Specifications Application and ID and Spark Plug Wire Inspection Testing and Inspection.
• If the spark plug wire resistance is greater than the specified value, replace the wire.
• If the spark plug wire tests normal, refer to Electronic Ignition System Diagnosis Electronic Ignition System Diagnosis for diagnosis of the ignition coil.
4. 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
* Cracked, worn, or incorrectly gapped-Refer to Spark Plug Inspection Testing and Inspection.
• If there is a condition with the spark plug, replace the spark plug.
5. Exchange the suspected spark plug with another cylinder that is operating correctly.
6. Operate the engine under the conditions in which the misfire occurred. This may include putting the engine under a load or allowing the engine to return to a cold condition. Observe the Misfire Current Counters with a scan tool. The misfire should not follow the spark plug exchange.
• If the misfire follows with the spark plug, replace the spark plug.
7. If all conditions test normal, test or inspect for the following:
* A lean or rich fuel injector-Refer to Fuel Injector Diagnosis .
* Verify that there is no misfire on cylinders 1, 4, 6, or 7 due to cylinder deactivation-Refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis Cylinder Deactivation (Active Fuel Management) System Diagnosis.
* An engine mechanical condition-Refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical.
Repair Instructions
* Spark Plug Replacement Service and Repair
* Spark Plug Wire Replacement Service and Repair
Repair Verification
1. Install any components that have been removed or replaced during diagnosis.
2. Clear the DTCs.
3. Turn OFF the ignition for 60 s.
4. 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 Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
5. Engine idling, observe the Misfire Current Cyl. 1-8 Counter parameters with a scan tool. The misfire current counter parameters should not be incrementing.
• If the misfire current counter parameters are incrementing, a misfire still exists.
6. 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 DTCs P0420 and P0430. Refer to DTC P0420 or P0430 P0420.