Component Location
General Description
The Misfire monitor diagnostic is based on crankshaft rotation velocity variation. The ECM determines crankshaft rotational velocity using the crankshaft position sensor and camshaft position sensor. When a cylinder misfires the crankshaft slows down momentarily. By monitoring the crankshaft and camshaft position sensor signals, the ECM can calculate when a misfire occurs. For a non-catalyst damaging misfire, the diagnostic will be required to report a misfire present within 1000-3200 engine revolutions. For catalyst damaging misfire, the diagnostic will respond to monitor 200 engine revolutions. Rough roads may cause false misfire detection. The rough road(acceleration)sensor consists of a piezoelectric vibration pick up which detects vertical acceleration of the vehicle. The sensor signal is used by the ECM to determine the degree of vertical movement of the car, for example, on a bumpy road. Since this may also cause uneven engine running, the ECM uses the signal to distinguish the phenomenon from actual 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 | Crankshaft speed fluctuation
| Contact resistance in connections.
Intake and Exhaust System
Ignition system
Fuel system
Adjustment of Timing
Faulty fuel injector
Faulty ECM
|
Case1 | Enable Conditions | Engine speed 400~4520 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
|
Case2 | Enable Conditions | Eng. load change = 41.2~200 %/cycle
Eng. speed change =21005~3300 rpm/s
Intake air temperature > -8.3?
|
Threshold Value | Misfire rate > 2.5~22.2% per 200 rev. (Depends on driving conditions)
|
Diagnostic Time | 200 rev
|
MIL ON Condition | Immediately (Blink)
|
Specification
InjectorCoil Resistance |
Primary Coil | Secondary Coil |
0.87± 10% ? | 13.0±15%? |