For 1990-2009 cars

### Circuit Description

DTCs P0301-P0304 are cylinder specific misfire codes. Each cylinder is monitored individually for a misfire condition and can set a cylinder specific diagnostic trouble code (DTC). The powertrain control module (PCM) uses the crankshaft position (CKP) sensor and camshaft position (CMP) sensor to determine engine misfire. The CKP sensor and the CMP sensor monitor their respective components and evaluate changes in the crankshaft rotational speed for each cylinder. Irregular changes in the crankshaft rotational speed indicate a possible misfire. The malfunction indicator lamp (MIL) illuminates when the misfire rate equals or exceeds a pre-determined count. A misfire rate that is high enough can cause the catalytic converter to overheat under certain driving conditions. The MIL will flash ON and OFF when the conditions for catalytic converter overheating are present.

### Conditions for Running the DTC

• | The engine speed is between 200-4,000 RPM.

• | The battery voltage is between 9-17 volts.

• | The engine coolant temperature (ECT) is between -7 to +123°C (20-254°F).

### Conditions for Setting the DTC

Misfire is indicated in engine cylinders 1-4.

### Action Taken When the DTC Sets

• | The PCM flashes the malfunction indicator lamp (MIL) the first time catalytic converter damage can occur.

• | The PCM illuminates the MIL the second time the diagnostic fails.

• | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. The PCM also freezes the engine speed at Misfire and the Load at Misfire scan tool data parameters at the time the MIL illuminates.

### Conditions for Clearing the MIL/DTC

• | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.

• | A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.

• | A DTC can be cleared by using the scan tool Clear DTC Information function.

### Diagnostic Aids

Check for any of the following conditions:

• | If any DTCs other than misfire (P0300 to P0304) are present, diagnose those DTCs first.

• | An intermittent ignition system malfunction may cause DTC P0301-P0304 to set. Check ignition system performance with an engine oscilloscope.

• | The scan tool data parameters Engine Speed at Misfire and Load at Misfire are fixed at the time the MIL illuminates. These scan tool displays can be used like additional lines of Freeze Frame data. Review the information located in the Engine Speed at Misfire and the Load at Misfire scan tool parameters. The information can help determine engine operation when the misfire occurred.

• | Review the misfire counters located in the Engine Data list of the scan tool while the engine is running. If the Total Misfire Current data parameter is increasing, the misfire condition is present. Misfire activity can be monitored with the scan tool in the Misfire Current Cyl # data list parameter of the appropriate cylinder. Use this information in order to determine if the fault is present or an intermittent malfunction.

• | An intermittent can also be the result of a defective CKP sensor signal rotor. Remove the CKP sensor and inspect the signal rotor through the sensor hole. Check the condition of the signal rotor for nicks, dents, missing teeth, and foreign material. Refer to Crankshaft Position Sensor Replacement .

• | Check for engine overheating. Refer to Engine Overheating in Engine Cooling.

• | A mass air flow (MAF) sensor output that is incorrect may cause the PCM to command the fuel system to go lean. Check the performance of the MAF sensor. If the heated oxygen sensor (HO2S) voltage is fixed low, while the fuel trim is constantly high, check the MAF sensor signal circuit for resistance. High circuit resistance can cause the sensor to read a lower volume of air than actual, resulting in a lean fueling condition that can cause engine misfire.

An intermittent malfunction may be caused by a fault in the electrical circuits of the ignition system or fuel system of the misfiring cylinder. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step verifies whether the misfire is present. The scan tool will display increasing counts in the Misfire Current Cyl. # parameter of the misfiring cylinder when a misfire is occurring.

3. This step checks whether the MIL is the result of a hard failure or an intermittent condition. Operating the vehicle in check mode enhances the diagnostic capabilities of the PCM. The scan tool will display increasing counts in the Misfire Current Cyl. # data parameter of the cylinder that is experiencing a misfire.

4. Fault not present indicates that the condition that caused the DTC P0301-P0304 to set is intermittent and not currently present. If no other DTCs are stored, refer to Diagnostic Aids for additional information on diagnosing an intermittent DTC P0301-P0304.

5. This step is to verify if the misfire is caused by a fault in the ignition system.

6. Contaminants in the fuel, such as alcohol or water, can create a misfire condition.

7. A vacuum leak can cause a lean misfire condition.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Install a scan tool.
2. Start the engine.
3. Monitor the Misfire Current Cyl. # data parameter for all engine cylinders on the scan tool.

Does the scan tool indicate a misfire in any cylinder?

--

Go to Step 5

Go to Step 3

3 |

1. Perform the scan tool Clear DTC Information function.
2. Place the vehicle into Check mode, using the scan tool. Refer to Service Bay Test .
3. Operate the vehicle within the Freeze Frame conditions as specified.
4. Monitor the Misfire Current Cyl. # data parameters on the scan tool.

Is a cylinder specific misfire DTC P0301-P0304 set or does the scan tool indicate a misfire in any cylinder?

--

Go to Step 5

Go to Step 4

4 | The fault is not present. Are there any DTCs stored that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Diagnostic Aids
5 | Is a DTC P1300, P1305, P1310, or P1315 present? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 6
6 |

1. Disconnect the ignition coil of the misfiring cylinder.
2. Remove the ignition coil of the misfiring cylinder. Refer to Ignition Coil Replacement .
3. Connect the electrical connector of the removed ignition coil .
4. Install a J 26792 Spark Tester or an equivalent at the end of the spark plug boot of the removed ignition coil.
5. Crank the engine while observing the J 26792 .
6. A crisp, blue spark should be observed.

Was a crisp, blue spark present on every engine revolution?

--

Go to Step 8

Go to Step 7

7 |

1. Turn OFF the ignition.
2. Exchange the ignition coil. Replace the ignition coil of the suspected faulty cylinder with an ignition coil from a normally operating cylinder.
3. Install the J 26792 or an equivalent at the end of the spark plug boot of the ignition coil.
4. Test for spark as performed in step 6.

Did the test indicate a crisp, blue spark while cranking the engine?

--

Go to Step 15

Go to Step 16

8 |

1. Perform a visual and physical inspection of the ignition coil boot for the following conditions:

• | Water intrusion or moisture

• | A corroded or damaged electrical terminal

• | Carbon tracking

2. Repair the condition or replace the ignition coil or spark plug as necessary. Refer to Ignition Coil Replacement or to Spark Plug Replacement .

Was a repair necessary?

--

Go to Step 18

Go to Step 9

9 |

1. Remove the spark plug from the misfiring cylinders. Refer to Spark Plug Replacement .
2. Inspect the spark plugs for correct operation and good performance. Refer to Spark Plug Inspection .
3. Repair or replace the spark plug as necessary. Refer to Spark Plug Replacement .

Was a faulty spark plug condition found and repaired?

--

Go to Step 18

Go to Step 10

10 |

1. Turn OFF the engine.
2. Disconnect the fuel injector of each misfiring cylinder.
3. Install a J 34730-2B Fuel Injector Test Lamp or an equivalent into the fuel injector harness connector of a misfiring cylinder.
4. Test the fuel injector circuit by observing the test lamp while cranking the engine.
5. Repeat the action in Step 3 and the test in Step 4 for each misfiring cylinder.

Did the fuel injector test lamp blink for every test while cranking the engine?

--

Go to Step 11

Go to Fuel Injector Circuit Diagnosis

11 | Perform the Fuel Injector Coil Test and the Fuel Injector Balance Test procedures. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and to Fuel Injector Balance Test with Special Tool .

Did any fuel injectors require replacement?

--

Go to Step 18

Go to Step 12

12 |

1. Turn OFF the ignition.
2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
3. Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
4. Install a scan tool.
5. Turn ON the ignition, with the engine OFF.
6. Select Fuel Pump in the Engine Output Controls menu of the scan tool.
7. Turn ON the fuel pump, using the scan tool.
8. Observe the fuel pressure indicated by the fuel pressure gage with the fuel pump running.

Is the fuel pressure within the specified range?

301-347 kPa (44-50 psi)

Go to Step 13

Go to Fuel System Diagnosis

13 |

1. Check a fuel sample for the following concerns:

• | Excessive alcohol content or contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Correct fuel type and quality

2. Replace the fuel as necessary. Refer to Fuel System Cleaning .

Was a repair necessary?

--

Go to Step 18

Go to Step 14

14 |

1. Visually and physically inspect the following for vacuum leaks:

• | The intake manifold gasket

• | The vacuum lines, hoses, and fittings

2. Repair any vacuum leaks as necessary.
3. Inspect the positive crankcase ventilation (PCV) system for an incorrectly operating or leaking PCV valve. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical.
4. Replace the PCV valve as necessary. Refer to Positive Crankcase Ventilation Valve Replacement in Engine Mechanical.

Did you replace a part or perform a repair?

--

Go to Step 18

Go to Step 17

15 | Replace the faulty ignition coil. Refer to Ignition Coil Replacement . Is the action complete? | -- | Go to Step 18 | --
16 |

1. Test the malfunctioning ignition coil circuits for the following conditions:

• | An open in the ignition coil ground circuit

• | An open in the positive voltage supply circuit

• | An open in the trigger signal circuit

• | No trigger signal generated by the PCM

2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems or to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 18

--

17 |

1. Check for the following engine mechanical conditions:

• | A worn or faulty camshaft

• | A leaky or sticky valve

• | Excessive valve deposits

• | Weak valve springs

• | A faulty valve lifter

• | An intake manifold runner leak or obstruction

• | Broken or worn piston rings

• | A leaking head gasket

2. Repair as necessary. Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Was a basic engine mechanical concern found and repaired?

--

Go to Step 18

Go to Diagnostic Aids

18 |

1. Perform the scan tool Clear DTC Information function.
2. Operate the vehicle within the Freeze Frame conditions that set the DTC.
3. Monitor the Misfire Current Cyl. # data parameters on the scan tool.

Did a DTC set or did the scan tool indicate a misfire in any cylinder?

--

Go to Diagnostic Trouble Code (DTC) List

System OK