P0305

DTC P0300

SYSTEM DESCRIPTION
The powertrain control module (PCM) 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 PCM 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 PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 sets.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected

CONDITIONS FOR RUNNING THE DTC
- DTCs P0016, P0101, P0102, P0103, P0107, P0108, P0116, P0117, P0118, P0120, P0125, P0128, P0220, P0315, P0335, P0336, P0340, P0341, P0608, P1125, P1516, P2101, P2108, P2120, P2125, P2135, or P2138 is not set.
- The engine speed is between 525-5,700 RPM.
- The ignition voltage is between 9-18 volts.
- The engine coolant temperature (ECT) is between -7 and +123°C (+19 and +253°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 PCM is not in fuel shut-off or decel fuel cut-off mode.
- The PCM is not receiving a rough road signal.
- The power management is not active.
- Excessive drive wheel slip is not detected.

CONDITIONS FOR SETTING THE DTC
The PCM 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 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 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. The control module illuminates the malfunction indicator lamp (MIL) when one of the following occur:
- The control module detects the same misfire failure during 2 consecutive trips.
- The control module detects any misfire failure during any subsequent trip if the conditions at the time of failure meet the following criteria:
- The engine load is within 20 percent of the previous test that failed.
- The engine speed is within 375 RPM of the previous test that failed.
- The engine coolant temperature is in the same range of the previous test that failed.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) at the beginning of the fourth ignition cycle, after 3 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 and related Freeze Frame data clears after 40 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
- Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:
- Variable thickness brake rotors-Refer to Symptoms - Hydraulic Brakes. Symptoms - Hydraulic Brakes
- Worn or damaged accessory drive belt-Refer to Symptoms - Engine. Symptom Related Diagnostic Procedures
- Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.
- If the condition is intermittent or not active, refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics

TEST DESCRIPTION

Step 1 - Step 8:

Step 9 - Step 21:

Step 22 - Step 24:

The number below refers to the step number on the diagnostic table.
2. If the actual crankshaft position (CKP) variation values are not within the learned values, the misfire counters may increment.