P0300
P0300Misfire detection - checksum error
Diagnostic conditions - V8
- Intake air temperature > -20 °
- Engine speed between 400 rpm...6500 rpm
- Load between 12 %...39 %
- No 'crankshaft sensor' fault code stored in memory
Diagnostic conditions - V6
- Intake air temperature > -20 °
- Engine speed between 520 rpm...6500 rpm
- Load between 12 %...34 %
- No 'crankshaft sensor' fault code stored in memory
Possible cause of fault
- Improper handling of a block heater
Fault in ignition system:
- Mechanical or electrical fault in spark plug
- Spark plug connector faulty
- Bar ignition module faulty
Fault in fuel/air mixture:
- Tank filled with incorrect fuel quality
- Tank driven empty
- Mechanical or electrical fault in injection valve
- Oxygen sensor faulty
- Fuel filter soiled
- Mechanical fault in fuel pump
Fault in exhaust system:
- Catalytic converter damaged (flow severely restricted)
- Kink in exhaust pipe
- Muffler faulty (flow severely restricted)
Fault in valve drive:
- Fault in timing adjustment of inlet camshaft (VarioCam)
- Outlet camshaft timing incorrect
- Hydro push rod faulty
- Valve seat or valve faulty
Fault in intake system:
- Leak in intake distributor
Affected pins
-
Diagnosis/troubleshooting
NOTE:
- The fault 'Misfire Detection Checksum Error' causes the Check Engine lamp to light up if exhaust-relevant misfires were detected in one or more cylinders in two consecutive journeys.
- An initial note appears because the relevant cylinder is stored.
NOTE:
- A cycle of 1,000 crankshaft revolutions is evaluated in the case of exhaust-related misfires (in the case of misfiring that causes damage to the catalytic converters, the cycle amounts to 200 revolutions). The misfiring rates are compared with a threshold value. If the misfiring rate is greater than the threshold value, the fault is set.
- The 'Check Engine' warning light is switched on (permanent light) if the misfiring rate exceeds the threshold value in two (or three in the case of EOBD) consecutive 'driving cycle' in which the emission limit values are exceeded.
- The 'Check Engine' warning light flashes if the misfiring rate has the potential to cause permanent catalytic converter damage. If the misfire rate is no longer reached during the first journey, the warning light goes out. If the rate is reached during the next journey, the warning light flashes. If this misfire rate is subsequently no longer reached, the warning light changes to a continuous light.
NOTE:
- When using a block heater (for heating the coolant), start and driving off difficulties or misfiring can occur if the block heater was connected for less than 4 hours.
- If the tank is driven empty, this can also lead to misfiring. The tank contents are therefore also stored in the event of misfire faults. If the tank was almost empty, there is probably no malfunction. Erase fault memory and carry out a test drive.
- In the event of a short circuit to B+ or ground in the oxygen sensors ahead of the catalytic converter, the mixture becomes too lean or too rich. This can cause misfiring. If an oxygen sensor fault ahead of the catalytic converter is also stored in memory, first correct this fault and then test drive the vehicle.
NOTE:
- If the battery was disconnected during troubleshooting or if the DME control module was removed, a sensor wheel must be adapted (range 1). It is only when this is done that misfires can be reliably detected by the DME.
- To do this, you must accelerate three times in fixed driving position Two and then allow the vehicle to coast to a stop, without switching the driving position or using the brake or accelerator (overrun fuel cut-off phase).
- To determine whether the adaptation was carried out, read out the 'Actual values" under the 'Adaptation status" menu item in the 9588 Porsche System Tester II.
