P0303

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
^ The Barometric Pressure (BARO) is more than 75 kPa.
^ The engine coolant temperature is more than -8°C (+18°F).
^ The intake air temperature is more than -8°C (+18°F).
^ The engine speed is less than 4,000 RPM.
^ The fuel tank level is more than 15 percent.
^ The Throttle Position (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.
^ The conditions are present for 5 seconds after engine start to 1 second from fuel shut-off.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM flashes the MIL the first time catalytic converter damage occurs.
^ The PCM illuminates the MIL the second time emission thresholds are exceeded or the 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 3 consecutively passing trips without a fault present.
^ A history DTC clears after 40 consecutive warm-up cycles without a fault.
^ Perform the scan tool Clear DTC Information function in order to clear the DTC.

DIAGNOSTIC AIDS
Check for 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. Engine Overheating
^ Any 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.
^ A fuel pressure that is out of specification. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ An intermittent ignition system malfunction in the spark plugs, the spark plug boots, or the ignition coils. Check the ignition system performance with an engine oscilloscope.
^ Inspect for the correct ignition timing and adjust as necessary. Refer to Ignition System Timing Adjustment Procedure. Adjustments
^ 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 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.

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

Steps 1-6:

Steps 7-12:

Steps 13-16:

The numbers below refer to the step numbers in the diagnostic table.
1. The Diagnostic System Check-Computers and Control Systems 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.
3. This step determines if a fault is present.
7. The ignition coil may have an internal fault.
9. 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.
10. A faulty fuel injector can cause a misfire condition and a DTC P0301 to set.
12. 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.
14. This step checks for a faulty CMP sensor signal rotor.