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P0300 is a diagnostic trouble code (DTC) for "Random/Multiple Cylinder Misfire Detected". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
Random/multiple cylinder misfire detected
Most vehicles will have 4-6 cylinders. Each cylinder will fire a spark plug, one after another, in a smooth and continuous manner. The spark plug fires a spark, using the flammable fuel air mixture, and sets fire to the fuel. The fuel then releases energy that powers the crankshaft, which must continuously turn smoothly as the car is moving.
If more than one cylinder misfires, this will increase or decrease the revolutions per minute (RPM) of the crankshaft. If that increase and/or decrease is more than 2 percent, the Powertrain Control Module will store the P0300 trouble code.
If the percentage of the increase or decrease in revolutions per minute (RPM) is between 2 percent and 10 percent, the Check Engine Light will come on. If the percentage of the increase or decrease in revolutions per minute (RPM) is greater than 10 percent, the Check Engine Light will blink on and off, as to alert the driver of a more serious misfiring problem. The P0300 trouble code indicates that there is a misfire in random or multiple cylinders.
Uses OBD-II scanner to retrieve freeze frame data and all of the trouble codes that have been stored by the Primary Control Module (PCM)
Completes a test drive of the vehicle to see if the P0300 trouble code comes back
Reviews live data to identify which cylinders are showing misfire data
Inspects spark plug wires or coil packs for wiring that is damaged or worn
Inspects spark plugs for excessive wear, cracks, or breaks
Inspects coil pack wiring at the harness and connector, for breaks, or corrosion
Replaces spark plugs, spark plug wires, coil packs, coil pack wiring at harness and connector, as necessary
If the P0300 trouble code is still present after the spark plugs, spark plug wires and/or coil packs have been replaced, they will inspect the fuel injectors and fuel injector system for faults
Older vehicles have a distributor cap and rotor button system. For these vehicles, the mechanic will inspect the distributor cap and rotor button for damage, cracks, or excessive wear
If other related trouble codes have been stored by the PCM, the mechanic will need to diagnose and repair these issues as necessary. Test drive the vehicle again to see if the P0300 trouble code comes back.
If the P0300 trouble code returns, the compression system should be checked. A fault in the compressor is rare but possible for this code.
If the P0300 trouble code still persists, there could be a problem with the PCM. This may require replacing or reprogramming. This is also rare.
One common mistake is ruling out the possibility of a faulty cylinder, fuel injector, or PCM. It is also common that the diagnosis and repair of other related trouble codes, is not completed.
Other related trouble codes, a faulty cylinder, a faulty fuel injector(s), and/or a faulty PCM can all cause the misfiring problem.
The P0300 trouble code is considered serious. The reason for this is the resulting driveability problems that are present when this trouble code is stored in the PCM. The car may not start and/or cause hazardous conditions during the operation of the vehicle. For these reasons, the P0300 trouble code requires immediate attention.
Do not assume that the spark plugs and wires are responsible for the P0300 trouble code. There are other components of the system that could cause this error code that should be diagnosed and inspected prior to repair.
Also, there are other related trouble codes that could cause the P0300. After repairs, if the P0300 trouble code returns, inspect and diagnose these other trouble codes if applicable. Always test drive the vehicle to see if the P0300 trouble code returns after making any repairs.
Make sure the spark plugs are gapped properly and with precision. To gap the spark plugs properly, it will be necessary to use a feeler gauge.
If the spark plug gap is not precise, this will cause a misfire.The vehicle manufacturer provides the spark plug gap specifications. These specifications can be found on a sticker under the hood of the vehicle or obtained from any local part store.
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