For 1990-2009 cars

### Circuit Description

DTCs P0301 through P0304 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

• | Barometric pressure is more than 75 kPa.

• | Engine coolant temperature is more than -7°C (19°F).

• | Intake air temperature is more than -7°C (19°F).

• | The engine must be running.

• | Engine speed is less than 4,000 RPM.

• | TP sensor change is less than 1 degree/10 ms.

### Conditions for Setting the DTC

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

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

• | Conditions present for 5 seconds after engine start.

### Action Taken When the DTC Sets

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

• | The PCM illuminates the MIL the second time emission thresholds are exceeded (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 three consecutively passing trips without a fault present.

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

• | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC.

### Diagnostic Aids

Check for any of the following conditions:

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

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

• | Check for engine vacuum leaks.

• | Inspect for correct operation of the EGR system. An EGR valve that is introducing too much exhaust gas into the combustion chamber can lower cylinder power output.

• | Check for malfunctioning fuel injectors. A poor fuel injector spray pattern can affect cylinder performance.

• | A fuel pressure that is out of specification. Refer to Fuel System Diagnosis .

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

• | A damaged wiring harness -- Inspect the applicable wiring harness for damage and repair as necessary.

• | A misfire DTC can also be the result of a defective crankshaft timing belt pulley. Remove the crankshaft position (CKP) sensor and inspect the crankshaft signal rotor through the sensor hole. Check the crankshaft timing belt pulley for foreign material or damaged teeth.

• | When the fault cannot be duplicated, wet the secondary ignition system of the suspect cylinder with water and operate the vehicle under the conditions that the DTC set.

If the DTC P0301 through P0304 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 P0304 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. The #1 ignition coil provides spark for cylinders 1 and 4 simultaneously. The #2 ignition coil provides spark for cylinders 2 and 3 simultaneously. Any condition that effects the ignition circuit of cylinder 4 may also have an affect on the ignition circuit of cylinder 1. Also any condition that effects the ignition circuit of cylinder 2 may also have an affect on the ignition circuit of cylinder 3. Inspect both sides of the ignition coil involved for cracks, carbon tracking, and corrosion.

4. The ignition coil may have an internal fault.

5. 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.

6. A faulty fuel injector can cause a misfire condition and a DTC to set.

7. 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. For diagnosis of an engine mechanical condition, refer to Engine Mechanical.

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

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-P0304 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 PCV valve--Refer to Crankcase Ventilation System Inspection .

• | 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 16

Go to Step 5

5 |

1. Install the J 26792 spark tester or an equivalent at the end of the spark plug boot of the misfiring cylinder.
2. Crank the engine while observing the spark tester.

Is a crisp, blue spark present?

Go to Step 9

Go to Step 6

6 |

1. Remove the ignition wire or ignition coil and boot of the misfiring cylinder.
2. Visually and physically inspect the ignition wire for a faulty condition. Refer to Spark Plug Wire Inspection .
3. Replace the ignition wire as necessary. Refer to Spark Plug Wire Replacement .
4. Visually and physically inspect the ignition coil and boot for any of the following conditions:

• | Carbon tracking

• | Insulation damage

• | Corroded terminals

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

Did you replace a part or perform a repair?

Go to Step 16

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. Repair as necessary.

Did you find and repair the condition?

Go to Step 16

Go to Step 8

8 | Replace the ignition coil. Refer to Ignition Coil Replacement . Did you complete the replacement? | Go to Step 16 | --
9 |

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 12

Go to Step 10

10 |

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 11

Go to Fuel Injector Circuit Diagnosis

11 | 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 16 | Go to Step 13
12 | Was a spark plug replaced because of fuel, oil, or coolant fouling? | Go to Step 13 | Go to Step 16
13 |

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 Diagnostic Starting Point - Engine Mechanical in Engine Mechanical.

Was a basic engine mechanical concern found and repaired?

Go to Step 16

Go to Step 14

14 |

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 16

Go to Step 15

15 |

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 16

Go to Diagnostic Aids

16 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 17

Go to Step 2

17 | 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