Component Location
General Description
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 monitors the crankshaft speed variation to determine if any misfiring generated. The ECM 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.
DTC Description
If a misfire exists that exceeds the threshold value, P0300 is set.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | Engine roughness through crankshaft speed fluctuation
| Poor connection Ignition system Fuel system Intake/exhaust air system Ignition timing Injector |
Case 1 | Enable Conditions | Engine speed 600~4520 rpm
Engine load > Zero torque line
|
Threshold Value | Misfire rate > 4.0% per 1000 rev.
|
Diagnostic Time | 1000 rev.
|
MIL ON Condition | 3 driving cycle
|
Case 2 | Enable Conditions | Eng. load change < 33%/s
Coolant temperature > -8.3?
Intake air temperature > -7.5?
|
Threshold Value | Misfire rate > 4.7~29.7%per 200 rev. (Depends on driving conditions)
|
Diagnostic Time | 200 rev.
|
MIL ON Condition | Immediately (Blink)
|