P0303

DTC P0303

DTC DESCRIPTOR

DTC P0300
Engine Misfire Detected

DTC P0301
Cylinder 1Misfire Detected

DTC P0302
Cylinder 2 Misfire Detected

DTC P0303
Cylinder 3 Misfire Detected

DTC P0304
Cylinder 4 Misfire Detected

DTC P0305
Cylinder 5 Misfire Detected

DTC P0306
Cylinder 6 Misfire Detected

DTC P0307
Cylinder 7 Misfire Detected

DTC P0308
Cylinder 8 Misfire Detected

DIAGNOSTIC FAULT INFORMATION
Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

If there are any other DTCs, diagnose those first. refer to Diagnostic Trouble Code (DTC) List - Vehicle. Diagnostic Trouble Code Descriptions

CIRCUIT/SYSTEM DESCRIPTION
The engine control module (ECM) uses information from the ignition control module (ICM) and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 sets. DTCs P0301-P0308 correspond to cylinders 1-8. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0220, P0222, P0223, P0315, P0335, P0336, P0340, P0341, P0608, P2135, or P2176 is not set.
- The engine speed is between 525-6,000 RPM.
- The ignition voltage is between 9-18 volts.
- The engine coolant temperature (ECT) is between -7 and +129°C (+19 and +264°F).
- If the ECT is less than -7°C (19°F) at engine start-up, the diagnostic will be disabled until the ECT is more than 21°C (69°F).
- The fuel level is more than 10 percent.
- The ABS and the traction control system (TCS) are not active.
- The transmission is not changing gears.
- The ECM is not in fuel shut-off or decel fuel cut-off mode.
- The ECM is not receiving a rough road signal.
- The power management is not active.
- Excessive drive wheel slip is not detected.
- DTCs P0300, and P0301-P0308 run continuously when the above conditions are met.

CONDITIONS FOR SETTING THE DTC
The ECM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
You must perform the CKP System Variation Learn Procedure before proceeding with this diagnostic procedure.

If condition is intermittent or not active, refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics

CIRCUIT/SYSTEM VERIFICATION
- There should be no abnormal engine noise.
- If there is abnormal engine noise. Refer to Symptoms - Engine. Symptom Related Diagnostic Procedures
- Diagnose any other DTCs that are set. refer to Diagnostic Trouble Code (DTC) List - Vehicle. Diagnostic Trouble Code Descriptions
- Observe the Misfire Current Counters with a scan tool.

IMPORTANT: If you cannot duplicate the conditions, operate the vehicle within the conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

- The engine should not be misfiring.

CIRCUIT/SYSTEM TESTING
1. Operate the engine within the conditions listed in the Freeze Frame Failure Records.
2. A current misfire should not be indicated.
- If a single cylinder Current Misfire is indicated, inspect the following components of the affected cylinder for proper operation:
- The ignition coil-Refer to Electronic Ignition (EI) System Diagnosis. Electronic Ignition (EI) System Diagnosis
- The spark plug-Refer to Spark Plug Inspection. Testing and Inspection
- The fuel injector-Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
- If there is still a single cylinder misfire, Refer to Symptoms - Engine. Symptom Related Diagnostic Procedures
- If more than one cylinder is randomly misfiring, inspect the following components condition and operation:
- The vacuum hoses and seals
- The throttle body and intake manifold
- The crankcase ventilation system-Refer to Crankcase Ventilation System Inspection/Diagnosis.
- The ECM grounds
- The exhaust system-Refer to Restricted Exhaust. Restricted Exhaust
- The fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis. Alcohol/Contaminants-in-Fuel Diagnosis
- The spark plugs-Refer to Spark Plug Inspection. Testing and Inspection
- If more than 1 cylinder is still misfiring, refer to Symptoms - Engine Symptom Related Diagnostic Procedures

REPAIR INSTRUCTIONS
Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

REPAIR VERIFICATION
If the customer concern was a flashing MIL, perform the following procedure:
1. Operate the vehicle at 2,500 RPM for 4 minutes.
2. Operate the vehicle within the Conditions for Running DTCs P0420 and P0430-Refer to DTC P0420. P0420
- If DTC P0420 or P0430 does not run and pass, diagnose those DTCs.
3. Clear the DTCs with a scan tool.
4. Turn OFF the ignition for 30 seconds.
5. Start the engine.
6. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
- If the DTC fails this ignition, a misfire still exists.