P0302

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 Setting the DTC
^ Engine coolant temperature greater than -7°C (19°F).
^ Intake air temperature less than -7°C (19°F).
^ Barometric pressure greater than 75 kPa.
^ Engine speed less than 4,000 RPM.
^ Fuel tank level greater than 15%.
^ TP sensor change is less than 1 degree / 10 ms.
^ Conditions present for 5 seconds after engine start to 1 second from fuel shut-off.

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.
^ Check for engine vacuum leaks.
^ Improper EGR system operation. Refer to EGR System Diagnosis.
^ A PCV system malfunction. Perform a functional check of the PCV valve. Refer to Crankcase Ventilation System Inspection.
^ Check for a malfunctioning fuel injector(s). Normal fuel injector resistance is 12-17 ohms at 20°C (68°F). Perform the Fuel Injector Coil Test/Balance Test Procedure if fuel injector resistance is out of specification. Refer to Fuel Inj Coil Test - ECT Between 10-35 Degrees C.
^ Fuel pressure that is out of specification. Refer to Fuel System Diagnosis.
^ An intermittent ignition system malfunction (spark plugs, ignition wires, ignition coil, and the distributor). Check ignition system performance with an engine oscilloscope.
^ 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 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.
If a DTC P0302 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. When the fault can not be duplicated, wet the secondary ignition system of the suspect cylinder with water and operate the vehicle under the conditions that the DTC set.

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. 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.
2. This step verifies whether the misfire is present.
3. This step verifies whether the misfire is caused by a hard failure or an intermittent. A misfire can sometimes be caused by a rough road condition.
8. This step checks for the proper clearance of the signal rotor. The signal rotor should have enough clearance to not contact other components when rotating. The signal rotor clearance is not adjustable. A damaged or improperly aligned signal rotor will require component parts replacement.
11. Contaminants in the fuel, such as alcohol or water, may cause a misfire condition.
22. Low engine compression and improper lash may also cause a rough idling condition. Refer to Engine Mechanical Diagnosis.