P0300
DTC P0300-P0304 (LUW)
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 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 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. DTCs P0301-P0304 corresponds 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 P0010, P0011, P0013, P0014, P0016, P0017, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0117, P0118, P0122, P0123, P0222, P0223, P0335, P0336, P0606, P0651, P0697, P06A3, P0806, P0807, P0808, P1104, P16F3, P182E, P2101, P2122, P2123, P2127, P2128, P2135 or P2138 are not set.
* The engine speed is between 500-6,500 RPM or DTC P0315 is set and the engine speed is greater than 1,000 RPM.
* The engine coolant temperature (ECT) is between -7 and +125°C (19 and 257°F).
* If the ECT is colder than -7°C (+19°F) at start-up, this diagnostic will not run until the ECT is between 21-125°C (70-257°F).
* The system voltage is between 9-32 V.
* The engine runtime is greater than 2 crankshaft revolutions.
* The throttle deltas are less than 95%.
* The fuel level is greater than 10%.
* The camshaft and crankshaft sensors are synchronized with each other.
* DTCs P0300-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 catalyst damaging levels to exceed mandated standards.
Action Taken When the DTC Sets
DTCs P0300-P0304 are Type B DTCs.
Conditions for Clearing the 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 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-Remove the drive belt and safely operate the engine to evaluate.
- 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.
* If the condition is intermittent, observing the scan tool IC Circuit Test and Fuel Injector Circuit Test Status parameters may help to isolate the condition. The circuit status parameters will change from OK or Not Run to Malfunction if a condition exists.
* A condition in HO2S heater control circuits may set a misfire DTC.
Reference Information
Schematic Reference
Engine Controls Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
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
* J 34730-2C - Injector Test light
* EL 26792 - HEI Spark Tester
For equivalent regional tools, refer to Special Tools Tools and Equipment.
Circuit/System Verification
1. Engine running at 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-P0204, P0315, P0335, P0336, P0351-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 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 are captured in the freeze frame/failure records lists.
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, refer to Crankcase Ventilation System Inspection/Diagnosis Testing and Inspection.
* 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 Testing and Inspection.
* 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 J 34730-2C - Injector Test light 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-P0204 (LUW) 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.
8. Install the EL 26792 - HEI Spark Tester between the spark plug boot of the misfiring cylinder and ground.
9. Connect the remaining wires to the appropriate cylinders.
Note: An erratic or weak spark is considered a no spark condition.
10. 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 (EI) System Diagnosis.
11. 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.
12. Exchange the suspected spark plug with another cylinder that is operating correctly.
13. Engine running, observe the scan tool Cylinder 1-4 Current Misfire Counters. The misfire should not follow the spark plug exchange.
• If the misfire follows the spark plug, replace the spark plug.
14. 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. Install any components or connectors that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming or setup procedures that are required when a component or module is removed or replaced.
3. Clear the DTCs.
4. Turn OFF the ignition for 60 s.
5. 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.
6. To verify that the performance of the catalyst has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to DTC P0420 P0420.