P0300-P0308 Error Codes Reasons & Explanation

What These Codes Mean:

All P030X codes indicate a misfire detected by the ECU.

A misfire =Fuel + Air + Spark did NOT burn correctly in a cylinder.

The ECU detects this using the crankshaft position sensor.
When a cylinder misfires, crankshaft speed slightly drops → ECU records it

Causes:

Bad ignition coil
Worn spark plug
Wrong spark plug gap
Oil in spark plug well
Coil connector loose
Coil overheating when hot
Clogged fuel injector
Stuck injector
Wrong injector installed
Low fuel pressure
Weak fuel pump
Dirty fuel filter
Vacuum leak near that cylinder
Intake manifold gasket leak
Burned valve
Low compression
Head gasket leak
Timing chain jumped
Large vacuum leak
Dirty MAF sensor
Low fuel pressure
EGR stuck open
Timing problem