ok so i did a little research and here's what i have found so far.
From the FSM, P0300 causes include:
- Improper spark plug
- Insufficient compression
- Incorrect fuel pressure
- The injector circuit is open or shorted
- Injectors
- Intake air leak
- The ignition secondary circuit is open or shorted
- Lack of fuel
- Drive plate or flywheel
- Heated oxygen sensor 1 (front)
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A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.
A code P0300 may mean that one or more of the following has happened:
* Faulty spark plugs or wires
* Faulty coil (pack)
* Faulty oxygen sensor(s)
* Faulty fuel injector(s)
* Burned exhaust valve
* Faulty catalytic converter(s)
* Stuck/blocked EGR valve / passages
* Faulty camshaft position sensor
* Defective computer
Possible Solutions
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.
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Nissan Technical Service Bulletin #NTB02-006 addresses the following codes for 2001 Pathfinders:
^ P0138
^ P0139
^ P0140
^ P0158
^ P0159
^ P0160
The bulletin states that if you have any of the codes, replace the incident O2 sensor. If you have codes P0138, P0139 or P0140, replace the rear RH O2 sensor with the following part, based on pro date:
Built up to 8/1/00: P/N: 226A0-4W001
Built on 8/2/00 or later: P/N: 226A0-4W010
The TSB also has you check the ECM part number and compare to a list of ECM part numbers on the bulletin, which will require the use of a CONSULT II scantool (meaning a trip to your Nissan dealer. Depending on the ECM program currently installed in your vehicle, it may need to be updated to the latest program revision.
Rear O2 sensors are for testing catalytic converter efficiency and have no affect on drivability, unlike the front O2 sensors, which the ECM uses to help provide the proper air/fuel ratio.
As far as O2 sensor identification, "Bank 1" is the engine bank that starts with #1 cylinder. "Sensor 1" is the front or "upstream" sensor. "Sensor 2" is the rear or "downstream" sensor. Bank 1 on the VQ engine is the right side bank and Bank 2 is the left side bank.
hopefully some can help me understand this a little bit more. any help is greatly appreciated.
