Refer to
Cell 21: Ignition System
and to
Cell 21: CMP Sensor and CKP Sensor
.
Circuit Description
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and from the camshaft position (CMP) sensor in order to determine if 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 if the misfire rate equals or exceeds a preset count. A misfire rate that is high enough can cause the catalytic converter to overheat under certain driving conditions. The MIL flashes on and off if the conditions for catalytic converter overheating are present.
Conditions for Running the DTC
| • | The engine coolant temperature is between -10°C and +110°C (14°F-230°F). |
| • | The intake air temperature is between -10°C and +70°C (14°F-158°F). |
| • | The barometric pressure is more than 75 kPa. |
| • | The TP sensor change is less than 1.9 degrees per 16 firing events. |
| • | The change in the manifold absolute pressure (MAP) is less than 1.3 kPa per 60 firing events. |
| • | The engine speed is less than 6,500 RPM. |
Conditions for Setting the DTC
| • | The misfire rate at 200 engine revolutions is more than a specified value. |
| • | The misfire rate at 1,000 RPM is more than a specified value. |
| • | The conditions are present from 5 seconds after the engine is started to 1 second before the fuel shut-off. |
Action Taken When the DTC Sets
| • | The PCM flashes the MIL the first time that catalyst damaging misfire occurs. |
| • | The PCM illuminates the MIL the second time emission thresholds are exceeded and the diagnostic fails. |
| • | The PCM records the operating conditions at the time that the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the DTC
| • | The MIL turns OFF after three consecutive trips during which the diagnostic runs and does not detect a fault. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the Clear DTC Information function of the scan tool, or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | If any DTCs beside misfire DTCs are present, diagnose those DTCs first. |
| • | Check for the engine overheating. |
| • | Check for engine vacuum leaks. |
| • | Check for a PCV system malfunction. Perform a functional check of the PCV valve. Refer to Crankcase Ventilation System Inspection . |
| • | Inspect the ignition system for an intermittent malfunction that is caused by the spark plugs, by the ignition wires, or by the ignition coil. Check the ignition system performance with an engine oscilloscope. |
| • | Determine if the fuel pressure is out of specification. Refer to Fuel System Diagnosis . |
| • | A fuel injector malfunction may cause DTC P0300 to set. Check the performance of the fuel injectors. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Sequential Multiport Fuel Injector Balance Test . |
| • | Water in the fuel may cause an intermittent misfire. Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | An engine mechanical malfunction.Measure the engine cylinder compression and the valve lash adjustment in order to compare the measurements to the OEM specifications. Refer to Engine Compression Test in Engine Mechanical. |
| • | Inspect the applicable wiring harness for damage, and repair the harness as necessary. |
| • | A misfire DTC may be the result of a faulty signal rotor on the crankshaft timing belt pulley. Remove the crankshaft position (CKP) sensor, and inspect the crankshaft signal rotor through the sensor hole. Check the crankshaft signal rotor for foreign material and for damaged teeth. |
| • | The PCM monitors the CKP sensor for engine reference signals. An erratic spark or an erratic fuel injector pulse may result without continuous accurate reference signals. An ignition reference low circuit for the CKP that is shorted to ground causes faulty engine reference signals to be sent to the PCM.The faulty signal will result in an engine misfire. Inspect the ignition reference low circuit for an intermittent short to ground. |
An intermittent fault may be induced by wetting the secondary ignition system with water before operating the vehicle under the conditions that caused the DTC to set.
If DTC P0300 cannot be duplicated, 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.
-
The Powertrain OBD System Check prompts the technician to complete some basic checks and to 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.
-
This step determines if a fault is present.
-
The ignition coil assemblies provide spark for two cylinders simultaneously. Any condition that affects the ignition circuit of one cylinder may also have an affect on the ignition circuit of the other paired cylinder. Inspect both sides of the ignition coil high voltage circuit for faulty conditions.
-
The ignition coil assemblies provide spark for two cylinders simultaneously. Any condition that effects the ignition circuit of one cylinder may also have an affect on the ignition circuit of the other paired cylinder. Inspect both sides of the ignition coil high voltage circuit for faulty conditions.
-
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 one cylinder may also have an affect on the ignition circuit of the other cylinder that shares the same coil. Inspect both sides of the ignition coil for cracks, carbon tracking, and corrosion.
-
The ignition coil may have an internal fault.
-
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.
-
Faulty fuel injectors can cause a misfire condition and a DTC P0300 to set.
-
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.
-
This step checks for faults in the CKP sensor and circuit that can cause incorrect ignition reference signals. Without continuous accurate reference signals, there is no dependable spark or fuel injector pulse. Erratic, missing, or incorrect engine reference signals can cause the engine to misfire.
-
This step checks for a faulty CKP sensor signal rotor. Visually inspect the teeth of the signal rotor through the CKP sensor aperture for damage, foreign material, and mis-alignment.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic System Check? | -- | |||||||||||||||||||||
2 | Start the engine. Is a misfire present at Idle? | -- | ||||||||||||||||||||
Is a DTC P0300 set? | -- | Go to Diagnostic Aids | ||||||||||||||||||||
4 |
Was a repair necessary? | -- | ||||||||||||||||||||
Did the test of each cylinder indicate a good crisp blue spark while cranking the engine? | -- | |||||||||||||||||||||
Was a repair necessary? | -- | |||||||||||||||||||||
7 |
Did any ignition wires need replacement? | 1.2k to 3.0k ohms/ft | ||||||||||||||||||||
Was a repair necessary? | -- | |||||||||||||||||||||
Replace the ignition coil that supplies the cylinder that had no spark. Refer to Ignition Coil Replacement . Is the action complete? | -- | -- | ||||||||||||||||||||
10 |
Did any spark plugs need replacement? | -- | ||||||||||||||||||||
Did the fuel injector test lamp flash for each fuel injector while cranking the engine? | -- | |||||||||||||||||||||
Check the 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 Sequential Multiport Fuel Injector Balance Test . Was a faulty fuel injector found and replaced? | -- | |||||||||||||||||||||
13 | Was the spark plug replaced because of fuel, oil, or coolant fouling? | -- | ||||||||||||||||||||
Was a basic engine mechanical concern found and repaired? | -- | |||||||||||||||||||||
Was a repair necessary? | -- | |||||||||||||||||||||
Was a repair necessary? | -- | Go to Diagnostic Aids | ||||||||||||||||||||
17 |
Are any DTCs displayed on scan tool? | -- | Go to the applicable DTC table | System OK |
