← Back to list

P0300 Fault on 1999 Nissan Pathfinder 4x4: Diagnosis and Fix (Solved)

Model: 1999 Nissan Pathfinder Fault Code: P0300 Posted: 2007-12-23 13:06

Hello, I recently performed an oil and air filter replacement on my 1999 Nissan Pathfinder 4x4. After starting the engine, the Service Engine Soon (SES) light began flashing. The issue only appeared when the vehicle was idle in Park, but disappeared while driving—despite the engine running smoothly. I used a diagnostic scanner and confirmed the fault code P0300: 'Random/Multiple Cylinder Misfire Detected.' I replaced the spark plugs with new Bosch platinum ones, but the flashing continued under idle conditions. The engine performs normally when in motion. After further investigation, I discovered that during a previous headlight replacement at night, I had to remove the air filter housing and reinstalled it without replacing the old, dirty filter. This may have introduced unmetered air into the intake system. Additionally, the timing belt was recently replaced by a mechanic for an oil leak repair. I checked all vacuum lines and confirmed they were properly connected. However, today the SES light flashed again with P0300 appearing. I am now concerned about whether the misfire is due to incorrect installation of the timing belt or faulty ignition components. What could be causing this persistent P0300 code in a 1999 Nissan Pathfinder? Any advice on proper spark plug types, ignition system checks, or sensor issues would be greatly appreciated. -Paul

Related fault codes

P0300

Comments (6)

Anonymous 2007-12-23 17:47

Ensure all vacuum hoses and connections were properly reattached during the air filter replacement—unmetered air can cause misfires. Also, verify that the manufacturer-specified spark plug type is being used. Using incorrect plugs may lead to poor combustion and misfire detection. Good luck and please update us on your findings.

Anonymous 2007-12-24 11:38

I initially installed 6 platinum Bosch spark plugs based on a Walmart catalog number—I don’t remember the exact part number. The issue started after replacing the driver-side headlight bulb at night. To access it, I had to remove the air filter and reattach the air filter housing without changing the old, dirty filter. After that, I took the car to a mechanic for an oil leak repair (crankshaft seal) and timing belt replacement. The engine ran fine after that. The next morning, the SES light began flashing after 5 minutes of idling. While driving, it turned off—engine performance remained normal. I scanned the system and confirmed P0300. I replaced both spark plugs and the air filter this time. Following your advice, I checked all vacuum lines—they were secure. However, today the SES light flashed again with P0300. What other potential causes could there be? Could it be related to the timing belt installation or ignition wiring?

Anonymous 2007-12-27 15:55

Start by using the manufacturer-recommended spark plugs—Bosch platinum types may not be optimal for this model. Also, inspect the ignition system carefully; during a tune-up, wires could have been damaged or improperly connected.

Anonymous 2007-12-27 21:32

The mechanic will check all wiring connections tomorrow. The SES light continues to flash only when the engine is idling in Park. I hope they identify the root cause and provide a fix. I’ll keep you updated on progress.

Anonymous 2007-12-28 12:23

You may also have a damaged sensor or an issue related to timing misalignment from the recent timing belt replacement—this wasn’t mentioned in your original post, but it’s worth considering as a potential cause of random cylinder misfires.

Anonymous 2007-12-28 22:16

The problem has been resolved. The root cause was an incorrect timing belt installation—one tooth off on the right-side camshaft. This misalignment caused the crankshaft position sensor to detect irregularities, triggering the P0300 code (flashing SES light). Although the engine ran normally during driving, this mechanical error led to the misfire detection. The mechanic corrected the timing belt installation at no cost—this was a mistake on their part. I’m now able to drive safely and will be heading to Los Angeles next Monday. Thanks for all the helpful suggestions. Wishing everyone a happy new year in 2008!