Refer to
Cell 21: Ignition System
and
Cell 21: CMP Sensor and CKP Sensor
.
Circuit Description
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.
Conditions for Running the DTC
| • | Engine coolant temperature is -10°C to 110°C (14°F to 230°F). |
| • | Intake air temperature is -10°C to 70°C (14°F to 158°F). |
| • | Barometric pressure is greater than 75 kPa. |
| • | TP sensor change is less than 1.9 degrees/16 firing events. |
| • | The change in MAP is less than 1.3 kPa / 60 firing events. |
| • | Engine speed is less than 6,500 RPM and the change in engine speed is less than 200 / 50 msec. |
Conditions for Setting the DTC
| • | The misfire rate at 200 engine revolutions is greater than a specified value. |
| • | The misfire rate at 1,000 engine revolutions is greater than a specified value. |
| • | The conditions are present for 5 seconds after the engine is started to 1 second from fuel shut-off. |
Action Taken When the DTC Sets
| • | The PCM flashes the malfunction indicator lamp (MIL) the first time a catalyst damaging misfire 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. |
| • | 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 . |
| • | An intermittent ignition system malfunction (spark plugs, ignition wires, ignition coil). Check ignition system performance with an engine oscilloscope. |
| • | Fuel pressure that is out of specification. Refer to Fuel System Diagnosis . |
| • | A fuel injector malfunction may cause a DTC P0304 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 . |
| • | Check for contaminated fuel. |
| • | An engine mechanical malfunction. Measure engine cylinder compression and valve lash adjustment for comparison to manufacture specifications. Refer to Engine Mechanical. |
| • | 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 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 or damaged teeth. |
An intermittent fault may be duplicated by wetting the secondary ignition system with water and operating the vehicle under the conditions that the DTC set.
If a 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.
-
The Powertrain 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.
-
This step determines if a fault is present.
-
The #1 ignition coil provides spark for cylinders 1 and 4 simultaneously. Any condition that effects the ignition circuit of cylinder 1 may also have an affect on the ignition circuit of cylinder 4. 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.
-
A faulty fuel injector can cause a misfire condition and a DTC P0304 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. For diagnosis of an engine mechanical condition, refer to Engine Mechanical.
-
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 P0304 set? | -- | Go to Diagnostic Aids | ||||||||||||||||||||||
4 |
Was a repair necessary? | -- | ||||||||||||||||||||||
5 |
Is a crisp, blue spark present? | -- | ||||||||||||||||||||||
6 |
Was a repair necessary? | -- | ||||||||||||||||||||||
7 |
Did the #4 ignition wire need replacement? | 3.0k to 6.7k ohms/ft | ||||||||||||||||||||||
Was a repair necessary? | -- | |||||||||||||||||||||||
Replace the #1 ignition coil. Refer to Ignition Coil Replacement . Is the action complete? | -- | -- | ||||||||||||||||||||||
10 |
Did the #4 spark plug need replacement? | -- | ||||||||||||||||||||||
Did the injector test lamp flash while cranking the engine? | -- | |||||||||||||||||||||||
Check the #4 fuel injector 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? | -- | |||||||||||||||||||||||
15 |
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 |
