P0300
DTC P0300
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 Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0300
- Engine Misfire Detected
Circuit/System Description
The engine control module (ECM) uses information from the crankshaft position sensor in order to determine when an engine misfire is occurring and uses information from the camshaft position sensor - intake and camshaft position sensor - exhaust sensors 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 catalyst 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.
Conditions for Running the DTC
* DTCs P0016, P0121, P0122, P0123, P0221, P0222, P0223, P0335 or P0336 are not set.
* The engine speed is between 600-6 528 RPM.
* The ECM is not in fuel cut-off mode.
* DTCs P0300, P0304, and P0313 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 catalyst damaging levels to exceed mandated standards.
Action Taken When the DTC Sets
DTC P0300 is a Type B DTC.
Conditions for Clearing the DTC
DTC P0300 is a Type B DTC.
Diagnostic Aids
* A misfire may only occur when the engine is under a load or when the engine is cold.
* A misfire DTC may 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
- Certain rough road conditions
- A damaged accessory drive component or belt
- A damaged reluctor wheel
* High resistance in the circuits of the injectors may set a misfire DTC without setting an injector DTC. Test the injector circuits of the affected cylinder(s) for a high resistance if you suspect a condition.
* The MIL indicator flashes when there is an engine misfire.
Reference Information
Schematic Reference
Engine Controls Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Sunshade - Left (D61)
Description and Operation
Fuel System Description Fuel System Description
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
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References for scan tool information
Special Tools
* EL 26792 - HEI Spark Tester
* EN 36012-A - Ignition System Diagnostic Harness
For equivalent regional tools, refer to Special Tools Tools and Equipment.
Circuit/System Verification
1. Engine running at the normal operating temperature, 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, P0202, P0203, P0204, P0315, P0335, P0336, P0351, P0352, P0353, or P0354 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 a load. An engine load may be necessary to verify the condition.
3. Observe the scan tool Misfire Current Counter parameters. The Misfire Current Counters should not be incrementing.
4. 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
1. Verify that the following conditions do not exist:
* Vacuum hose splits, kinks, and incorrect connections
* Engine vacuum leaks
* Crankcase ventilation system for vacuum leaks
* Fuel pressure that is too low or too high, refer to Fuel System Diagnosis Fuel System Diagnosis.
* Contaminated fuel, refer to Alcohol/Contaminants-in-Fuel Diagnosis 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, disconnect the harness connector at the appropriate Q17 Fuel Injector.
3. Connect a test lamp between the control circuit terminal 2 and the ignition voltage circuit terminal 1.
4. Engine idling, the test lamp should flash.
• If the test lamp does not flash, refer to DTC P0201, P0202, P0203, P0204, P0261, P0262, P0264, P0265, P0267, P0268, P0270, or P0271 P0201.
5. Ignition OFF, connect the Q17 Fuel Injector connector. Remove the T8 Ignition Coil.
6. Inspect the ignition coil spark plug boots for the following conditions:
* Damage
* Carbon tracking
* Oil contamination
* Water intrusion
• If you find any of the above conditions, repair as necessary.
7. Connect the harness connector to the ignition coil assembly.
Note: It may be necessary to secure the EN 36012-A - ignition system diagnostic harness to the spark plug boots with electrical tape.
8. Install the EN 36012-A - ignition system diagnostic harness to the spark plug boots.
9. Install the EL 26792 - HEI spark tester between the spark plug boot of the misfiring cylinder and ground.
10. Connect the remaining wires to the appropriate cylinders.
Note: An erratic or weak spark is considered a no spark condition.
11. Attempt to start the engine and observe the EL 26792 - HEI spark tester. The spark tester should spark.
• If there is no spark, refer to Electronic Ignition System Diagnosis Electronic Ignition System Diagnosis.
12. Ignition OFF, remove the spark plug from the misfiring cylinder. Verify the following conditions do not exist with the spark plug:
* Gas, coolant, or oil fouled, refer to Spark Plug Inspection Testing and Inspection.
* Cracked, worn, incorrectly gapped
• If there is a condition with the spark plug, replace the spark plug.
13. Exchange the suspected spark plug with another cylinder that is operating correctly.
14. Engine running, observe the scan tool Misfire Current Counters. The misfire should not follow the spark plug exchange.
• If the misfire follows the spark plug, replace the spark plug.
15. If all conditions test normal, test or inspect for the following:
* A lean or rich fuel injector, refer to Fuel Injector Diagnosis Fuel Injector Diagnosis.
* An engine mechanical condition, refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical.
Repair Instructions
* Ignition Coil Replacement Service and Repair
* Spark Plug Replacement Service and Repair
Repair Verification
1. If the customer concern was a flashing MIL, operate the vehicle within the conditions for running DTC P0420. Refer to DTC P0420 P0420.
2. Clear the DTCs with a scan tool.
3. Turn OFF the ignition for 60 s.
4. Start the engine.
5. 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.
6. If the DTC fails this ignition, a misfire still exists.