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P0303




DTC P0300-P0306

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

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 sensor and the camshaft position sensors in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM detects individual misfire events. A misfire rate that is high enough can cause 3-way catalytic converter damage. The malfunction indicator lamp (MIL) flashes 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 is set, and the corresponding fuel injector is disabled. To retest for a misfire, the ECM re-enables the fuel injector(s) after 4 crankshaft revolutions or after 8 crankshaft revolutions for manual transmission equipped vehicles. For catalyst damaging misfires the ECM re-enables the fuel injector(s) after a 30 second delay to retest for a misfire. This 30 second periodic re-enabling occurs until the end of the drive cycle or until no further catalyst damaging misfire events are present.

Conditions for Running the DTC

* DTC P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, or P0338 is not set.
* The engine speed is between 400 and 7,000 RPM.
* The engine coolant temperature (ECT) is warmer than -30°C (-22°F).
* The delivered torque signal is greater than 6 % at idle, transmission not in drive.
* The delivered torque signal is between 7 and 29 % with the transmission in drive.
* The evaporative emissions (EVAP) leak detection is not active.
* The ECM is not in fuel cut-off or decel fuel cut-off mode.
* The fuel level is greater than 11 %.
* The clutch pedal is not depressed, vehicles equipped with manual transmissions.
* DTCs P0300 through P0306 run continuously when the above conditions exist for at least 1,000 engine revolutions.
* DTCs P0300 through P0306 run continuously when the above conditions exist and the ECT is warmer than 47°C (117°F) for at least 1,000 engine revolutions for the first failure occurance, 200 engine revolutions after the fist failure occurance for catalyst damaging misfire(s).

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.

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.

Action Taken When the DTC Sets

* DTCs P0300-P0306 are Type B DTCs.
* When the MIL is flashing, the injector may be disabled for the misfiring cylinder to protect the catalytic converter.
* Depending on the conditions that set the code, the engine may go into Open Loop.

Conditions for Clearing the DTC

* DTCs P0300-P0306 are Type B DTCs.
* The DTC must pass under the same conditions that were present when the DTC failed.

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; remove the belt and safely operate the engine to evaluate

* 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 isolate the condition. The circuit test status parameters will change from OK or Not Run to Fault if a condition exists.

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 (Powertrain Component Views)

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 - Spark Tester
* For equivalent regional tools, refer to Special Tools (Tools and Equipment).

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 no other DTCs are set.

• If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).

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. 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).
* Exhaust system restrictions

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

2. Ignition OFF, remove the T8 ignition coil of the misfiring cylinder, but leave 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. Install the J 26792 - Spark Tester to the boot of the appropriate T8 ignition coil and ground.

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

5. Attempt to start the engine and observe the J 26792 - Spark Tester. 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.

6. 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 (Application and ID).

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

7. Exchange the suspected spark plug with another cylinder that is operating correctly.
8. 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.

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

* A lean or rich Q17 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 (Ignition Coil Replacement - Bank 1)
* Ignition Coil Replacement - Bank 2 (Ignition Coil Replacement - Bank 2)

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 Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) and perform the appropriate diagnostic procedure.
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 DTC P0420 or P0430. Refer to DTC P0420 or P0430 (P0420).

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