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P0300




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 startup 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. Refer to Crankshaft Position System Variation Learn Testing and Inspection.

* Ensure that each fuel injector is connected to the proper fuel injector harness connector. Refer to Engine Controls Schematics (L99/LS3) [1][2]Electrical DiagramsEngine Controls Schematics (LSA) [1][2]Electrical Diagrams

* A high resistance condition on any fuel injector control circuit can cause an engine misfire P0300-P0308 DTC to set without setting a fuel injector circuit P0201-P0208 DTC.

* A high resistance condition on any ignition control (IC) circuit can cause an engine misfire P0300-P0308 DTC to set without setting an IC circuit P0351-P0358 DTC.

* A misfire may only occur when the engine is operating under a load or when the engine is cold.

* 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 (L99/LS3) [1][2]Electrical DiagramsEngine Controls Schematics (LSA) [1][2]Electrical Diagrams

Connector End View Reference

Component Connector End Views Fuel Pump and Level Sensor Assembly - Primary

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 Control Module References for scan tool information

Special Tools

J 26792 - HEI Spark Tester

For equivalent regional tools, refer to Special Tools (Diagnostic Tools) Special Tools (Diagnostic Tools).

Circuit/System Verification

1. Engine idling, 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-P0208, P0315, P0335, P0336, P0351-P0358 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 load. An engine load may be necessary to verify the condition.

* Random misfires that are not steadily incrementing may be normal.

3. Engine idling, observe the Cylinder 1-8 Current Misfire Counter parameters with a scan tool. The misfire counter parameters should not be incrementing.

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 (L99/LS3) [1][2]Electrical DiagramsEngine Controls Schematics (LSA) [1][2]Electrical Diagrams.

* Engine vacuum leaks

* Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis (Without Super Charger) Fuel System Diagnosis (Without Super Charger)Fuel System Diagnosis (With Super Charger) Fuel System Diagnosis (With Super Charger).

* 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. 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 - HEI spark 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 - HEI spark 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 [1][2]Specifications and Spark Plug Wire Inspection Testing and Inspection.

• If the spark plug wire resistance is not the specified value, replace the wire.

• If the spark plug wire tests normal, refer to Electronic Ignition System Diagnosis Electronic Ignition (EI) 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 (CH47976) Fuel Injector Diagnosis (CH47976)Fuel Injector Diagnosis (J39021 or Scan Tool) Fuel Injector Diagnosis (J39021 or Scan Tool).

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

Repair Instructions

* Spark Plug Replacement Service and Repair

* Spark Plug Wire Replacement Service and Repair

Repair Verification

1. Install any components that have been removed or replaced during diagnosis.

2. Clear the DTCs.

3. Turn OFF the ignition for 60 s.

4. 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 and perform the appropriate diagnostic procedure.

5. Engine idling, observe the Cylinder 1-8 Current Misfire Counter parameters with a scan tool. The misfire counter parameters should not be incrementing.

• If the misfire counter parameters are incrementing, a misfire still exists.

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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