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

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.

Conditions for Running the DTC

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 4 seconds or for a cumulative of 50 seconds.

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 4 seconds or for a cumulative of 50 seconds.

Action Taken When the DTC Sets

DTCs P0300, P0301, P0302, P0303, P0304, P0305, and P0306 are Type A (MIL flashing) or Type B1 DTCs.

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:

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 HEI Spark Tester

Circuit/System Verification

1. Engine idling at the normal operating temperature. Verify there is no abnormal engine noise.

⇒	If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical .

2. Verify that DTCs: DTC P0011, P0014, P0021, P0024, P0201-P0206, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0335, P0336, P0338, P2088, P2090, P2092, P2094, P2300, P2301, P2303, P2304, P2306, P2307, P2309, P2310, P2312, P2313, P2315, or P2316 are not set.

⇒	If any of the listed DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

3. Observe the scan tool Misfire Current Cyl 1-6 parameters. The Misfire Current Counters should not be incrementing.
4. Engine idling, perform the scan tool cylinder power balance test in order 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 are captured in the Freeze Frame/Failure Records Data List.

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 .

•	Contaminated Fuel--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•	Exhaust system restrictions

⇒	If you find any of the above conditions, repair as necessary.

2. Ignition OFF, remove the ignition coil from the misfiring cylinder, with the electrical connector connected.
3. 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.

4. Remove the fuel pump fuse.
5. Install the J 26792 to the boot of the ignition coil and ground.

Important: An erratic or weak spark is considered a no spark condition.

6. Attempt to start the engine and observe the J 26792 . The spark tester should spark.

⇒	If there is no spark, refer to Electronic Ignition (EI) System Diagnosis for diagnosis of the ignition coil.

7. Ignition OFF, remove the spark plug from the misfiring cylinder. Verify the spark plug does not exhibit the following conditions:

•	Gas, coolant, or oil fouled--refer to Spark Plug Inspection .

•	Cracked, worn, or incorrectly gapped--refer to Ignition System Specifications .

⇒	If there is a condition with the spark plug, replace the spark plug.

8. Exchange the suspected spark plug with another cylinder that is operating correctly.
9. Engine idling, 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.

10. If all conditions test normal, test or inspect for the following:

•	A lean or rich fuel injector--Refer to Fuel Injector Solenoid Coil Test .

•	An engine mechanical condition--Refer to Symptoms - Engine Mechanical .

Repair Instructions

Repair Verification

1. If the customer concern was a flashing malfunction indicator lamp (MIL), refer to DTC P0420 or P0430 .
2. Ignition ON, 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 are captured in the Freeze Frame/Failure Records Data List.

⇒	If the DTC fails this ignition, a misfire still exists.