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P0308




DTC P0300-P0308

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

DTC P0307
- Cylinder 7 Misfire Detected

DTC P0308
- Cylinder 8 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 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 catalytic converter to overheat, possibly damaging the converter. The malfunction indicator lamp (MIL) will flash ON and OFF when catalytic converter overheating conditions are present and DTC P0300 is set. DTCs P0301-P0308 corresponds to cylinders 1-8. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will also set.

Conditions for Running the DTC

* DTC P0010, P0011, P0016, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0122, P0123, P0128, P0220, P0222, P0223, P0335, P0336, P0606, P0641, P0651, P1516, P2101, P2119, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P2176, P3401, P3425, P3441, and P3449 are not set.
* The engine speed is between 375-5,800 RPM and DTC P0315 is not set.
OR
* The engine speed is greater than 1,000 RPM and DTC P0315 is set.
* The ignition voltage is between 9-18 V.
* The engine coolant temperature (ECT) is between -7 and +125°C (+19 and +257°F).
* If the ECT is less than -7°C (+19°F) at start-up this diagnostic will not run until the ECT is more than +21°C (+69°F).
* The fuel level is more than 10 %.
* The antilock brake system (ABS) and the traction control system are not active or detecting rough road.
* The power management is not active.
* The ECM is not in fuel shut-off, or decel fuel cut-off mode.
* Excessive drive wheel slip is not detected.
* Torque Converter Clutch (TCC) is not applied/active.
* The cylinder deactivation is not in progress, where applicable.
* A manual transmission with a throttle position less than 95 %.
* DTCs P0300-P0308 run continuously when the above conditions are met.

Conditions for Setting the DTC

DTC P0300

The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed mandated standards.

DTC P0301, P0302, P0303, P0304, P0305, P0306, P0307, or P0308

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-P0308 are Type B DTCs.
* When the MIL is flashing the fuel injector may be disabled for the misfiring cylinder to protect the catalytic converter.
* Depending on the conditions that set the DTC, the engine may go into Open Loop.

Conditions for Clearing the MIL/DTC

* DTCs P0300-P0308 are Type B DTCs.
* The DTC must run and pass under the same operating conditions that were present when the DTC failed.

Diagnostic Aids

* The Crankshaft Position System Variation Learn procedure may need to be performed.
* Ensure that each fuel injector is connected to the proper fuel injector harness connector.
* A misfire may only occur when the engine is operating under a load or when the engine is cold.
* A high resistance condition on any ignition control circuit can cause an engine misfire P0300-P0308 DTC to set without setting an ignition control circuit P0351-P0358 DTC.
* This test procedure requires that the vehicle battery has passed a load test and is completely charged. Refer to Battery Inspection/Test (Battery Inspection/Test).
* A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect the following for possible sources of vibration:

- A tire or wheel that is out of round or 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
- A damaged reluctor wheel

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)

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

Circuit/System Verification

1. 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).

2. Engine idling, verify there is no abnormal engine noise.

• If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical (Symptoms - Engine Mechanical).

3. Observe the Cylinder 1-8 Current Misfire Counters with a scan tool. The Current Misfire Counters should not be incrementing. Random misfires that are not steadily incrementing may be normal.
4. Operate the vehicle within the Conditions for Running the DTC to verify that 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

Note: You must perform the Circuit/System Verification first.

1. Verify that the following conditions do not exist:

* The fuel injector wire harness electrical connectors are connected to the wrong fuel injectors. Refer to Engine Controls Schematics ([1][2]Electrical Diagrams).
* Engine 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 (Special Tool) (Alcohol/Contaminants-In-Fuel Diagnosis (Special Tool))Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) (Alcohol/Contaminants-In-Fuel Diagnosis (Without Special Tool)).
* Restricted exhaust system-Refer to Restricted Exhaust (Restricted Exhaust).

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

2. Verify that there is no misfire on cylinders 1, 4, 6, or 7 due to cylinder deactivation-Refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis (Cylinder Deactivation (Active Fuel Management) System Diagnosis).
3. Ignition OFF, install the J 26792 - Tester to the spark plug wire boot of the misfiring cylinder.

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

4. Attempt to start the engine and observe the J 26792 - Tester. The spark tester should spark.

• If there is no spark, test the spark plug wire for the correct resistance, refer to Ignition System Specifications (Application and ID) and Spark Plug Wire Inspection (Testing and Inspection).
• If the spark plug wire tests normal, refer to Electronic Ignition System Diagnosis (Electronic Ignition System Diagnosis) for diagnosis of the ignition coil.

5. Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the following conditions do not exist with the spark plug:

* Gas, coolant, or oil fouled
* Cracked, worn, or incorrectly gapped-Refer to Spark Plug Inspection (Testing and Inspection).

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

6. Exchange the suspected spark plug with another cylinder that is operating correctly.
7. Operate the engine under the conditions in which the misfire occurred. This may include putting the engine under a load or allowing the engine to return to a cold condition. Observe the Misfire Current Counters with a scan tool. The misfire should not follow the spark plug exchange.

• If the misfire follows with the spark plug, replace the spark plug.

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

* A lean or rich fuel injector-Refer to Fuel Injector Diagnosis (J39021 or Tech 2) (Fuel Injector Diagnosis (J39021 or Tech 2))Fuel Injector Diagnosis (CH47976) (Fuel Injector Diagnosis (CH 47976)).
* An engine mechanical condition-Refer to Symptoms - Engine Mechanical (Symptoms - Engine Mechanical).

Repair Instructions

* Spark Plug Wire Replacement (Service and Repair)
* Spark Plug Replacement (Service and Repair)

Repair Verification

1. Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
2. 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 Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) for DTC P0420 or P0430.

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