For 1990-2009 cars

Refer to

#### Ignition System

Engine Controls Components
Cell 20: CMP and CKP Sensors
Cell 20: A/T Controls Inputs
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Cell 10: Ignition Switch, IGN Fuse, and ST Fuse
Cell 14: G105 and G106 (1 of 2)
and

#### Cell 20: Fuel Injectors

Engine Controls Components
Cell 20:Engine Data Sensors
Cell 20: Fuel Supply System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Cell 10: Ignition Switch, IGN Fuse, and ST Fuse
schematics.

### Circuit Description

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 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. Each cylinder is monitored individually for a misfire condition. A DTC P0300 indicates that engine misfire was indicated in more than one cylinder at the same time.

### Conditions for Running the DTC

• | Engine speed is between 200 and 4,000 RPM.

• | Battery voltage is between 9 volts and 17 volts.

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

### Conditions for Setting the DTC

Misfire is indicated in more than one cylinder simultaneously.

### 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 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. The PCM also freezes two scan tool data list parameters related to the misfire condition. The Engine Speed at Misfire and the Load at Misfire scan tool data parameters are fixed 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 Information function.

### Diagnostic Aids

Check for the following conditions:

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

• | If DTCs P0301, P0302, P0303, or P0304 are also present with a DTC P0300, diagnose those DTCs first.

• | An intermittent ignition system malfunction (spark plugs, ignition wires, ignition coil) may cause a DTC P0300 to set. Check ignition system performance with an engine oscilloscope.

• | The Engine Speed at Misfire and the Load at Misfire scan tool data parameters are fixed at the time the MIL illuminates. These two scan tool displays can be used like two additional lines of Freeze Frame data. Review the Engine Speed at Misfire and the Load at Misfire scan tool parameters located on the scan tool Engine Data list. The information can help determine the vehicle conditions 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 Count data parameter is being populated (count increasing), the misfire condition is present. A current DTC P0300 should indicate misfire activity in the Total Misfire Current Count parameter. Use this information in order to determine if the fault is present now, or is 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.

• | Check for engine overheating.

• | Check for a PCV system malfunction. Perform a functional check of the PCV valve. Refer to Crankcase Ventilation System Inspection .

An intermittent malfunction may be caused by a fault in the ignition system or fuel system electrical circuits. Inspect the wiring harness and components for any of the following conditions:

• | Backed out terminals.

• | Improper mating of terminals.

• | Broken electrical connectors locks.

• | Improperly formed or damaged terminals

• | Faulty terminal to wire connections.

• | Physical damage to the wiring harness.

• | A broken wire inside the insulation.

• | Corrosion of electrical connections, splices, or terminals.

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 in the Diagnostic Table.

1. The OBD System Check 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 Total Misfire Current Count parameter if a misfire is occurring.

3. This step checks whether the DTC P0300 is the result of a hard failure or an intermittent condition. Operating the vehicle in check mode enhances the PCM's diagnostic capabilities. For additional information on check mode operation refer to the Powertrain Control Module Diagnosis section. The scan tool will display increasing counts in the Total Misfire Current Count parameter if a misfire is occurring.

4. This step is to verify if the misfire is cause by a fault in the ignition system.

5. This step checks for a faulty signal rotor. A faulty signal from the CKP sensor can cause the ignition system to misfire. Visually inspect the signal rotor through the CKP sensor aperture for damaged teeth, missing teeth, foreign material, and mis-alignment.

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 | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install a scan tool.
2. Start the engine.
3. Monitor the Total Misfire Current Count parameter on the scan tool.

Did the scan tool indicate any misfire counts?

--

Go to Step 4

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.
3. Operate the vehicle within the Freeze Frame conditions as specified.
4. Monitor the Total Misfire Current Count parameter on the scan tool.

Did a DTC P0300 set or did the scan tool indicate any misfire counts?

--

Go to Step 4

Fault not Present-Go to Diagnostic Aids

4 |

1. Connect a J 26792 spark tester or an equivalent at the spark plug end of #1 ignition wire.
2. Crank the engine and observe the spark tester.
3. A crisp, blue spark should be observed.
4. Repeat steps 1 thru 3 for each of the ignition wires.

Is spark present at each ignition wire?

--

Go to Step 8

Go to Step 5

5 |

1. Remove any ignition wire that failed to produce a crisp, blue spark.
2. Inspect each suspect ignition wire for any of the following conditions:

• | Check with a DMM that the resistance of each ignition wire does not exceed the specified value.

• | Check for carbon tracking inside the plug wire boots.

• | Check for damage to the boots or cable insulation.

Did any of the ignition wires fail any of the above inspections?

25,000 ohms (25k ohms)

Go to Step 15

Go to Step 6

6 |

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

• | Cracks on the coil towers

• | Water intrusion

• | Faulty ignition wire terminal connection

• | Carbon tracking

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

Was a repair necessary?

--

Go to Step 17

Go to Step 7

7 |

1. Remove the CKP sensor. Refer to Crankshaft Position Sensor Replacement .
2. Visually inspect the CKP sensor signal rotor for the following conditions:

• | Damaged or missing teeth

• | Foreign material

• | Correct installation

3. Repair as necessary.

Was a repair necessary?

--

Go to Step 17

Go to Step 14

8 |

1. Remove the spark plugs.
2. Visually and physically inspect the spark plugs for any of the following conditions:

• | Oil fouling

• | Fuel fouling

• | Evidence of coolant in the cylinder

• | Incorrect gap

• | Loose center electrode

• | Cracked porcelain

• | Carbon tracking

• | Loose terminal end

3. Replace as necessary.

Did any of the spark plugs need replacement?

--

Go to Step 17

Go to Step 9

9 |

1. Turn OFF the ignition.
2. Disconnect all four fuel injector electrical connectors.
3. Install a J 34730-2B fuel injector test lamp or an equivalent into each fuel injector harness connector.
4. Observe the injector test lamp for each fuel injector while cranking the engine.

Did the fuel injector test lamp flash for each injector while cranking the engine?

--

Go to Step 10

Go to Fuel Injector Circuit Diagnosis

10 | 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 Fuel Injector Balance Test . Did any fuel injectors require replacement? | -- | Go to Step 17 | Go to Step 11
11 |

1. Turn OFF the ignition.
2. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
3. Install a fuel pressure gauge. Refer to Fuel Pressure Gage Installation and Removal .
4. Install a scan tool.
5. Turn ON the ignition, leaving 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 gauge with the fuel pump running.

Is the fuel pressure within the specified value?

301-347 kPa (44-50 psi)

Go to Step 12

Go to Fuel System Diagnosis

12 |

1. Check a fuel sample for the following concerns:

• | Alcohol or other contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Fuel type and quality.

2. Replace the fuel as necessary.

Was a repair necessary?

--

Go to Step 17

Go to Step 13

13 |

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

• | The PCV valve.

• | The intake manifold gasket.

• | The vacuum lines, hoses, and fittings.

2. Repair any vacuum leaks as necessary.

Was a repair necessary?

--

Go to Step 17

Go to Step 16

14 | Replace the faulty ignition coil. Refer to Ignition Coil Replacement . Is the action complete? | -- | Go to Step 17 | --
15 | Replace any spark plug wires that were found to be faulty. Is the action complete? | -- | Go to Step 17 | --
16 |

1. Check for any of the following engine mechanical concerns:

• | Worn or faulty camshaft

• | Leaky or sticky valves

• | Excessive valve deposits

• | Weak valve springs

• | Incorrect valve timing

• | Intake manifold runner leaks or obstructions

• | Broken or worn piston rings

• | Leaking head gasket

2. Repair as necessary. Refer to Engine Compression Test in Engine Mechanical.

Was a basic engine mechanical concern found and repaired?

--

Go to Step 17

Go to Diagnostic Aids

17 |

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 Total Misfire Current Count parameter on the scan tool.

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

--

Go to the Applicable DTC Table

System OK