P0300 indicates the PCM has detected multiple random cylinder misfires.  This code may be accompanied with cylinder specific misfire codes.  If present, the following codes my be helpful in determining which cylinders are at fault.

  • P0301 - Cylinder number one misfire
  • P0302 - Cylinder number two misfire
  • P0303 - Cylinder number three misfire
  • P0304 - Cylinder number four misfire
  • P0305 - Cylinder number five misfire
  • P0306 - Cylinder number six misfire
  • P0307 - Cylinder number seven misfire
  • P0308 - Cylinder number eight misfire 


Seven common problems that cause OBD trouble code P0300:

The following is a list of problems that can cause a P0300 code in the order we feel is most likely to occur.  Certainly, each situation is different and there are other possible reasons for random cylinder misfires, but these are most common. 

1) Fouled, cracked, worn or otherwise misfiring spark plugs

2) Bad ignition wires - burnt, cracked, carbon tracked wires or plug boots

3) Defective ignition components - ignition module, ignition coil, distributor cap, etc..

4) Vacuum leaks

5) Defective fuel injector(s)

6) Low fuel level or low fuel pressure

7) Internal mechanical engine faults 


Here are some other, more obscure causes we've seen (in no particular order)

  • Cracked flexplate
  • EGR valve stuck open
  • Defective cam or crank position sensor
  • loose timing chain
  • Poor fuel quality - water in gas tank
  • Engine excessively overfilled with oil
  • Uneven EGR flow caused by carbon build-up on engine with multiple EGR ports
  • loose or corroded fuel injector wiring



Related Pages...

Performing Injector Balance Tests to find problem cylinders