Misfires can be caused by lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or many other causes. Even a small number of misfires may result in excessive exhaust emissions due to the unburned mixture. Increased misfire rates cause damage to the catalytic converter. The ECM/PCM monitors the crankshaft speed variation to determine if any misfiring generated. The ECM/PCM identifies the specific cylinder in which the misfire has occurred and counts individual misfire events by monitoring changes in the crankshaft rotation for each cylinder. A random misfire indicates one or more cylinders are misfiring.
If a misfire exists that exceeds the threshold value, P0300 is set.
Item | Detecting Condition | Possible Cause | |
DTC Strategy |
•
Engine roughness through crankshaft speed fluctuation | 1. Poor connection 2. Ignition system 3. Fuel system 4. Intake/exhaust air system 5. Ignition timing 6. Injector | |
Case1 | Enable Conditions |
•
510 rpm ＜ Engine speed ＜ 4500rpm
•
Engine load > Zero torque line | |
Threshold Value |
•
Misfire rate > 3% per 1000 rev. | ||
MIL ON Condition |
•
3 driving cycle | ||
Case2 | Enable Conditions |
•
510 rpm ＜ Engine speed ＜ 4500rpm
•
Engine load > Zero torque line | |
Threshold Value |
•
Misfire rate > 5~33% per 200 rev. (Depends on driving conditions) | ||
MIL ON Condition |
•
Immediately (Blink) | ||
