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Failed Smog Test

Nissan Pathfinder Trouble Code OBDII P0300

1996 Nissan Pathfinder LE Trouble Code P0300 - My Nissan Pathfinder failed the smog test because the check engine light came on during the test with trouble code P0300. All other components were pass. Random/Multiple misfires doesn't really tell me much. Can you suggest a course of action.


A P0300 is a difficult OBDII trouble codes to diagnose. A P0300 indicates a random or multiple misfire. A P0300 does not point to any one engine cylinder nor does it explain the reason for the misfire. It is up to a smog check technician or mechanic to diagnose the components which might be causing an engine misfire.

Some symptoms of trouble code P0300 include, hard starting engine, engine stumble and/or engine hesitate. If there are no symptoms, we recommend you reset the code and see if it comes back. If your Nissan Pathfinder has not had problems in the past and P0300 was triggered during the smog check and never before, we recommend resetting the code.

Trouble Code OBDII P0300 may indicate one or more of the following has occurred:

  • Faulty spark plugs or wires
  • Faulty ignition coil
  • Faulty oxygen sensor(s)
  • Faulty fuel injector(s)
  • Faulty catalytic converter(s)
  • Faulty EGR valve / passages
  • Faulty camshaft position sensor
  • Defective computer (ECU)

If there are engine symptoms such as hesitating or stumbling, then there is obviously an engine problem which needs to be diagnosed and repaired prior to your next smog inspection.

We recommend you check all wiring that lead to the cylinders. In other words, inspect the spark plugs, spark plug wires, coil, distributor and so on. Depending on how old your Nissan Pathfinder's ignition components are, it may be a good idea to replace them as part of your regular maintenance schedule. We recommend replacing spark plugs, spark plug wires, distributor cap, and rotor.

posted by SmogTips Support 11-21-2013 12:55 PM

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