Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
The P0300 code means that a cylinder(s) is misfiring or is randomly misfiring. Start by checking for intake leaks, intake gaskets are common causes of multi-cylinder misfiring. If no leaks are found the next step is to replace the spark plugs. If the problem persists more tests need to be done to diagnose the problem, see "Possible Causes".
The cost to diagnose the P0300 2003 NISSAN ALTIMA SEDAN code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the Crankshaft Position (CKP) sensor signal to vary, the Engine Control Module (ECM) can determine that a misfire is occurring. The Diagnostic Trouble Code (DTC) will be set when the Engine Control Module monitors the crankshaft speed and has detected a misfire condition
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