P0303

DTC P0300-P0308

Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
• Review Strategy Based Diagnosis for an overview of the diagnostic approach. Initial Inspection and Diagnostic Overview
• Diagnostic Procedure Instructions provides an overview of each diagnostic category. Initial Inspection and Diagnostic Overview

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 (CKP) sensor in order to determine when an engine misfire is occurring, and uses information from the camshaft position (CMP) 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
• DTCs P0010, P0011, P0016, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0220, P0222, P0223, P0335, P0336, P0606, P1516, P2101, P2120, P2122, P2123, P2125, P2127, P2128, P2135, P2138, P215B, and P2176 are not set.
• DTCs P2160 and P2161, where applicable, are not set.
• When DTC P0315 is set, the engine speed must be more than 1,000 RPM.
• Engine run time is more than 2 crankshaft revolutions.
• The engine speed is between 375-5,600 RPM.
• The ignition voltage is between 9-18 volts.
• The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F).
• When the startup ECT is colder than -7°C (+19°F), this diagnostic will be delayed until the ECT is warmer than +21°C (+69°F).
• The fuel level is more than 10 percent.
• The ECM is not in fuel shut-off, or decel fuel cut-off mode.
• The electronic brake control module (EBCM) and the traction control system (TCS) are not active.
• An automatic transmission shift with a throttle position more than 95 percent is not occuring.
• The power management is not active.
• Excessive drive wheel slip is not detected.
• The power take-off (PTO) is disabled, where applicable.
• The cylinder deactivation is not in progress, where applicable.
• DTCs P0300-P0308 run continuously when the above conditions are met.

Conditions for Setting the DTC

DTC P0300
The ECM is detecting a crankshaft speed change indicating a random misfire is occuring that exceeds mandated emission level standards or is at catalytic converter damaging levels.

DTC P0301, P0302, P0303, P0304, P0305, P0306, P0307, or P0308
The ECM is detecting a crankshaft speed change indicating a single cylinder misfire is occuring that exceeds mandated emission level standards or is at catalytic converter damaging levels.

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
• 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 (IC) circuit can cause an engine misfire DTC P0300-P0308 to set without setting an IC circuit DTC P0351-P0358.
• 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
- A damaged accessory drive component or belt
- A damaged reluctor wheel
- The Crankshaft Position System Variation Learn procedure may need to be performed.

Reference Information

Schematic Reference
Engine Controls Schematics

Connector End View Reference
Component Connector End Views Connector Views

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 for scan tool information Control Module References

Special Tools
J 26792 HEI Spark Tester

Circuit/System Verification
1. Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description.

2. Ignition ON, verify the scan tool hood position parameter displays Open.
--> If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F. Diagnostic Trouble Code (DTC) List - Vehicle

3. 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

4. Engine idling, verify there is no abnormal engine noise.
--> If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical. - Symptoms - Engine Mechanical

5. Observe the Misfire Current Counters with a scan tool. The Misfire Current Counters should not be incrementing. Random misfires that are not steadily incrementing may be normal.

6. 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

Important: 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.
• 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.
• 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 Description

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, and Spark Plug Wire Inspection.
--> If the spark plug wire tests normal, refer to 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.
--> 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. Component Tests and General Diagnostics
• An engine mechanical condition--Refer to Symptoms - Engine Mechanical. - Symptoms - Engine Mechanical

Repair Instructions
• Spark Plug Wire Replacement
• Spark Plug Replacement

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 seconds.

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 and perform the appropriate diagnostic procedure. Diagnostic Trouble Code (DTC) List - Vehicle

5. 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
Refer to DTC P0430