P0300

DTC P0300

System Description

The engine control module (ECM) 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 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 overheating and damage to the 3-way catalytic converter (TWC) under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC damage are present. If the ECM detects a misfire rate sufficient to cause emission levels to exceed a predetermined value, DTC P0300 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0300 Engine Misfire Detected

Conditions for Running the DTC

* DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0315, P0336, P0337, P0341, P0342, and P0502 are not set.

* The engine is operating for more than 10 seconds.

* The camshaft position sensor is sychronized with the crankshaft.

* The engine speed is between 600-6,500 RPM and steady.

* The ignition 1 voltage is between 11-16 volts.

* The engine coolant temperature (ECT) is between -7°C and +120°C (+19°F and +248°F).

* The fuel level is more than 15 percent.

* The throttle angle is steady within 10 percent.

* The throttle angle is less than 4 percent when the vehicle speed is more than 10 km/h (6 mph)

* The antilock brake system (ABS) and the traction control system (TCS), if equipped, is not active.

* The torque management is not active.

* The transmission is not changing gears.

* The A/C clutch is not changing states.

* The ECM is not in fuel shut-off or decel fuel cut-off mode.

* The ECM is not receiving a rough road signal.

* DTC P0300 runs continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed a predetermined value.

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

Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:

* A tire or wheel that is out of round or out of balance

* Variable thickness brake rotors

* A unbalanced or damaged driveline condition

* Certain rough road conditions

* Worn or damaged accessory drive component or belt

For an intermittent condition, refer to Intermittent Conditions Intermittent Conditions.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2.

This step determines if there is a current misfire condition. The scan tool will display increasing counts in the Total Misfire Current Counter parameter if a misfire is occurring.

3.

If the Total Misfire Current Counter parameter is incrementing, but the engine is NOT misfiring, this could be caused by an excessive vibration from other sources than the engine.

4.

If the actual CKP variation values are not within the learned values, the Total Misfire Current Counter parameter may increment.