For 1990-2009 cars

### Circuit Description

DTCs P0301 through P0306 are cylinder specific misfire codes. The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring changes in the crankshaft rotation for each cylinder the PCM counts individual misfire events. 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.

### Condition for Running the DTC

• | The barometric pressure (BARO) is more than 75 kPa.

• | The engine coolant temperature is more than -8°C (+18°F).

• | The intake air temperature is more than -8°C (+18°F).

• | The engine speed is less than 4,000 RPM.

• | The fuel tank level is more than 15 percent.

• | The throttle position (TP) sensor change is less than 1 degree/10 ms.

### Conditions for Setting the DTC

• | The misfire rate at 200 engine revolutions is more than a specified value.

• | The misfire rate at 1,000 engine revolutions is more than a specified value.

• | The conditions are present for 5 seconds after engine start to 1 second from fuel shut-off.

### Action Taken When the DTC Sets

• | The PCM flashes the MIL the first time catalytic converter damage occurs.

• | The PCM illuminates the MIL the second time emission thresholds are exceeded or 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.

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after 3 consecutively passing trips without a fault present.

• | A history DTC clears after 40 consecutive warm-up cycles without a fault.

• | Perform the scan tool Clear DTC Information function in order to clear the DTC.

### Diagnostic Aids

Check for the following conditions:

• | If any DTCs other than misfire (P0300 to P0306) are present, diagnose those DTCs first.

• | Check for engine overheating

| Refer to Engine Overheating in Engine Cooling.

• | Any engine vacuum leaks.

• | A fuel pressure that is out of specification

| Refer to Fuel System Diagnosis .

• | A sticking or leaking ERG valve

| Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .

• | Incorrect ignition timing

| Refer to Ignition System Timing Adjustment .

• | An intermittent ignition system malfunction in the spark plugs, the ignition wires, or the ignition coils--Check the ignition system performance with an engine oscilloscope.

• | An intermittent engine misfire may be caused by ignition system components that are susceptible to moisture. Spray water on the ignition system components and wiring in order to check for an engine miss or crossfire.

Check for other intermittent conditions. Refer to Intermittent Conditions .

If the DTC P0301 through DTC P0306 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the applicable cylinder specific misfire trouble code on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC appears in the Not Ran Since Code Cleared list, the diagnostic for that particular DTC has not yet run. When the DTC no longer appears in the Not Ran Since Code Cleared list, the DTC diagnostic has run. If the MIL is NOT ILLUMINATED, and there is no PENDING DTC Status in DTC Information, the cylinder specific misfire diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

If a DTC P0301 through DTC P0306 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

### Test Description

The numbers below refer to the step numbers in 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 determines if a fault is present.

3. This step checks the ignition coil for external faults.

4. This step checks for the electrical signal from the PCM for the operation of the fuel injector. If the injector test lamp does not illuminate, the fuel injector control circuit is diagnosed for a faulty condition.

5. A faulty fuel injector can cause a misfire condition and a cylinder specific misfire DTC to set.

6. This step checks for a mechanical fault as the cause of the misfire condition. Low engine compression and improper valve lash may also cause a rough idling condition.

7. This step checks for a faulty CMP sensor signal rotor.

8. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTCs P0301 through DTC P0306 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0301 through DTC P0306 appear in the Not Ran Since Code Cleared list, the DTC P0301 through DTC P0306 diagnostic has not yet run. When DTC P0301 through DTC P0306 does not appear in the Not Ran Since Code Cleared list, the DTC P0301 through P0306 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0301 through DTC P0306 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

Step | Action | 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 | Start the engine. Is a misfire present at idle? | Go to Step 4 | Go to Step 3
3 |

1. Install a scan tool.
2. Turn ON the ignition, leaving the engine OFF.
3. Clear the scan tool information.
4. Operate the vehicle within the Freeze Frame data as noted.

Did a DTC P0301-P0306 set?

Go to Step 4

Go to Diagnostic Aids

4 |

1. Perform a visual and a physical inspection for any of the following conditions:

• | Incorrectly operating or leaking positive crankcase ventilation (PCV) valve. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical 2.5L.

• | Incorrect PCV valve

• | A vacuum leak at the intake manifold or gasket

• | A vacuum leak at a cracked, split, or worn vacuum hose

2. Repair as necessary.

Did you find and repair the condition?

Go to Step 15

Go to Step 5

5 |

1. Remove the ignition coil of the suspect cylinder. Refer to Ignition Coil Replacement .
2. Connect the electrical connector to the ignition coil.
3. Install the J 26792 Spark Tester or an equivalent at the end of the spark plug boot of the ignition coil.
4. Crank the engine while observing the spark tester.

Does the spark tester indicate a crisp blue spark while cranking the engine?

Go to Step 8

Go to Step 6

6 |

1. Visually and physically inspect the ignition coil boot for any of the following conditions:

• | Carbon tracking

• | Insulation damage

• | Corroded terminals

2. Replace the ignition coil boot as necessary. Refer to Ignition Coil Replacement .

Did you replace a part or perform a repair?

Go to Step 15

Go to Step 7

7 |

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

• | Cracks

• | Moisture

• | Faulty electrical connections

• | Carbon tracking

• | Corrosion

2. Replace the ignition coil and boot as necessary. Refer to Ignition Coil Replacement .

Did you complete the replacement or repair?

Go to Step 15

Go to Electronic Ignition (EI) System Diagnosis

8 |

1. Remove the spark plug from the misfiring cylinder. Refer to Spark Plug Replacement .
2. Visually and physically inspect the spark plug for a faulty condition. Refer to Spark Plug Inspection .
3. Replace as necessary. Refer to Spark Plug Replacement .

Did any spark plug need replacement?

Go to Step 11

Go to Step 9

9 |

1. Turn OFF the ignition.
2. Disconnect the fuel injector of each misfiring cylinder.
3. Install a J 34730-2B Injector Test Light 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 flash for every test while cranking the engine?

Go to Step 10

Go to Fuel Injector Circuit Diagnosis

10 | Test all suspect fuel injectors for proper operation. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test with Special Tool . Were any faulty fuel injectors found and replaced? | Go to Step 15 | Go to Step 12
11 | Was a spark plug replaced because of fuel, oil, or coolant fouling? | Go to Step 12 | Go to Step 15
12 |

1. Check for any of the following engine mechanical concerns that could affect a misfiring cylinder:

• | Worn or faulty camshaft

• | Leaking or sticking valves

• | Excessive valve deposits

• | Broken or leaking piston rings

• | Weak valve springs

• | Incorrect valve timing

• | Intake (vacuum) leaks

• | Leaking head gasket

• | Loose or broken motor mount

2. Repair as necessary. Refer to Symptoms - Engine Mechanical in Engine Mechanical 2.5L.

Was a basic engine mechanical concern found and repaired?

Go to Step 15

Go to Step 13

13 |

1. Remove the CMP sensor. Refer to Camshaft Position Sensor Replacement .
2. Visually inspect the CMP sensor for the following conditions:

• | Physical damage

• | Foreign material on the sensor (magnet) surface

• | Water or corrosion at the electrical terminals

3. Repair as necessary.

Did you find and repair the condition?

Go to Step 15

Go to Step 14

14 |

1. Visually inspect the CMP sensor signal rotor in the camshaft sensor housing for the following conditions:

• | Damaged teeth

• | Foreign material

• | Correct installation

2. Repair as necessary.

Did you find and repair the condition?

Go to Step 15

Go to Diagnostic Aids

15 |

1. Turn OFF the ignition.
2. Remove the DOME fuse for 30 seconds.
3. Install the DOME fuse.
4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
5. Start the engine.
6. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or until the DTCs P0301 through P0306 diagnostic test has run.

Does the DTC run and pass?

Go to Step 16

Go to Step 2

16 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | Go to Diagnostic Trouble Code (DTC) List | System OK