DTC P0300 Unidentified Engine Misfire Detected
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BMW Technical Information System
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This Diagnostic Trouble Code (DTC P0300) is the Powertrain Control Module (PCM) way of telling us that it has found multiple misfires, but it can not identify which cylinders they are. If there were DTCs such as P0301 through P0310, that would identify a single cylinder that is the culprit and would narrow your focus of diagnostics.
The Powertrain Control Module (PCM) uses the Crankshaft Position Sensor pulses to determine the position (cylinder) and the rpm of the engine at various degrees of rotation. The crankshaft of the engine will increase in velocity as each cylinder fires. Less velocity increase from one cylinder as compared to the others indicates a misfire.
The Powertrain Control Module (PCM) can use this information and can control which cylinders fire and thus determine what percentage of misfire is being caused by each cylinder.
If the misfire is drastic enough to cause catalyst damage the Powertrain Control Module (PCM) will start flashing the Malfunction Indicator Lamp (MIL). The Malfunction Indicator Lamp (MIL) will be on steady if an emissions failure is recorded.
The Malfunction Indicator Lamp (MIL) will be commanded off if after three consecutive passed trips meeting the original failure criteria or after 80 passed trips if the criteria has not been met.
Since the PCM can not identify which cylinders are misfiring, you need to go to basics and check everything that would be considered common, like loose or broken air duct tubing, vacuum leaks, malfunctioning Positive Crankcase Ventilation (PCV) system, Ignition Coils (multi coil system), ignition cables, spark plugs, distributor cap and rotor, EGR valve, engine compression, lack of maintenance (VVT engine), etc.
You should check for Technical Service Bulletins (TSB) including those that address the possible need to reprogram the Powertrain Control Module (PCM) that may relate to the Diagnostic Trouble Code (DTC P0300). If it needs reprogrammed that can be performed with J2534 tools such as ours.
Fix It Right The First Time!
Fortunately, everything you need everything you need to fix it right the first time is right here!
To access the sensor and data from your Engine Controller (PCM) you will need:
Professional Quality Scan Tool such as our 2X80S Scan Tool series.
Professional Quality Automotive Diagnostic Software such as OBD2 Spy, OBD 2007, or Scan Master.
If you understand how the systems were designed to work and how to test them, great! Otherwise you will need factory product service training manuals that will teach you and guide you through the diagnostic phase.
You might also need the manufacturer factory service manuals and data systems that provide specifications and details relative to your specific model.
Or aftermarket data systems such as All Data, Mitchell On Demand, Auto Data, Bosch, and others.
Everything is available here for you as a single source for all your needs. The aftermarket data systems are available in our members only area by direct shipment from the distributor at great pricing.
