P0303
DTC P0300-P0306
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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
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) sensors 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. DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set, and the corresponding fuel injector is disabled. The ECM will re-enable the fuel injector after 4 crankshaft revolutions when the misfire is not current. The ECM will re-enable the fuel injector after 8 crankshaft revolutions when the misfire is not current, if the vehicle is equipped with a manual transmission.
Conditions for Running the DTC
* DTC P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, or P0338 is not set.
* The engine speed during engine start is greater than 450 RPM.
* The ECM detects greater than 5 ignition events after start-up.
* The engine speed is between 420-7,000 RPM and steady.
* The engine load is between 10-29 percent dependent on engine speed.
* The startup engine coolant temperature (ECT) is warmer than -30°C (-22°F).
* The ECM is not receiving a rough road signal.
* The throttle angle is steady.
* The ECM is not in fuel cut-off or decel fuel cut-off mode.
* DTCs P0300 through P0306 run continuously when the above conditions exist.
Conditions for Setting the DTC
P0300
The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value for greater than 1,000 crankshaft revolutions, 200 crankshaft revolutions for catalyst damaging misfire.
P0301, P0302, P0303, P0304, P0305, P0306
The ECM detects a crankshaft rotation speed variation indicating a single cylinder misfire rate sufficient to cause emissions levels to exceed mandated standards for greater than, 1,000 crankshaft revolutions, 200 crankshaft revolutions for catalyst damaging misfire.
Action Taken When the DTC Sets
* DTCs P0300, P0301, P0302, P0303, P0304, P0305, and P0306 are Type A (MIL flashing) or Type B DTCs.
* The ECM may disable the fuel injector of the misfiring cylinder when a misfire is present.
Conditions for Clearing the DTC
DTCs P0300, P0301, P0302, P0303, P0304, P0305, and P0306 are Type A (MIL flashing) or Type B1 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
- Transmission operation
- A damaged accessory drive component or belt
* The ignition coils for each bank are fused separately. If a fuse opens or the ignition voltage circuit opens between the fuse and the splice, all the ignition coils for one bank of the engine would be inoperative. If the ground circuit opens at the engine block, the ignition coils would be inoperative for one bank of the engine.
Reference Information
Schematic Reference
Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Special Tools
J 26792 HEI Spark Tester
Circuit/System Verification
1. Engine idling at the normal operating temperature.
• If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical (- Symptoms - Engine Mechanical).
2. Verify that DTC P000A-P000D, P0011, P0014, P0021, P0024, P0087, P0088, P0089, P0201-P0206, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P029D, P02A1, P02A5, P02A9, P02AD, P02B1, P0335, P0336, P0338, P0351-P0356, P2088, P2090, P2092, P2094, P2146, P2149, P2152, P2155, P216A, P216D, P2300, P2301, P2303, P2304, P2306, P2307, P2309, P2310, P2312, P2313, P2315, or P2316 is not set.
• If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions).
3. Observe the scan tool Misfire Current Cyl. 1-6 parameters. The Misfire Current Counters should not be incrementing.
4. Engine idling, perform the cylinder power balance test with a scan tool to isolate the misfiring cylinder. The engine speed should change when each injector is disabled.
5. 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. Ignition OFF, open the hood to disable the Auto-Stop function.
2. Ignition ON, verify the scan tool hood position parameter displays Open.
• If the hood position does not display Open, refer to DTC P254F (P254F).
3. 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 (with Special Tool) (Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool))Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) (Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool))
* Exhaust system restrictions
• If you find any of the above conditions, repair as necessary.
4. Ignition OFF, remove the ignition coil of the misfiring cylinder, with the electrical connector connected.
5. Inspect the ignition coil boot for the following conditions:
* holes
* tears
* carbon tracking
* oil contamination
* water intrusion
• If you find any of the above conditions, repair as necessary.
6. Remove the fuse that supplies voltage to terminal 32 of the fuel pump control module (FPCM).
7. Install the J 26792 to the boot of the appropriate ignition coil and ground.
Note: An erratic or weak spark is considered a no spark condition.
8. Attempt to start the engine and observe the J 26792 . The spark tester should spark.
• If there is no spark, refer to Electronic Ignition System Diagnosis (Electronic Ignition System Diagnosis) for diagnosis of the ignition coil.
9. Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the spark plug does not exhibit the following conditions:
* Gas, coolant, or oil fouled-Refer to Spark Plug Inspection (Testing and Inspection).
* Cracked, worn, incorrectly gapped-Refer to Ignition System Specifications (Specifications).
• If there is a condition with the spark plug, replace the spark plug.
10. Exchange the spark plug with another cylinder that is operating correctly.
11. Install the fuse that supplies voltage to terminal 32 of the fuel pump control module (FPCM).
12. Engine idling, observe the scan tool Misfire Current Counter parameters. The misfire should not follow the spark plug exchange.
• If the misfire follows the spark plug, replace the spark plug.
13. If all conditions test normal, test or inspect for the following:
* A lean or rich fuel injector-Refer to Fuel Injector Solenoid Coil Test (Fuel Injector Solenoid Coil Test)
* An engine mechanical condition-Refer to Symptoms - Engine Mechanical (- Symptoms - Engine Mechanical).
Repair Instructions
* Spark Plug Replacement (Service and Repair)
* Ignition Coil Replacement - Bank 1 (Service and Repair)
* Ignition Coil Replacement - Bank 2 (Service and Repair)
Repair Verification
1. If the customer concern was a flashing malfunction indicator lamp (MIL), refer to DTC P0420 or P0430 (P0420).
2. Clear the DTCs with a scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. 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.
• If the DTC fails this ignition, a misfire still exists.