Possible causes

– Faulty spark plug 4
– Clogged or faulty fuel injector 4
– Faulty ignition coil 4
– Fuel injector 4 harness is open or shorted
– Fuel injector 4 circuit poor electrical connection
– Ignition coil 4 harness is open or shorted
– Ignition coil 4 circuit poor electrical connection
– Insufficient cylinder 4 compression
– Incorrect fuel pressure
– Intake air leak

Tech notes

The P0304 code means that the cylinder 4 is misfiring or is randomly misfiring. Start by checking for intake leaks an if no leaks are found the next step is to replace the spark plugs on cylinder 4. If the problem persist more tests needs to be done to diagnose problem, see “Possible Causes”

When is the code detected?

Engine Cylinder 4 is Misfiring.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Lack/loss of power
– Hard start
– Engine hesitation

P0304 Description

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.

P0304 Information for specific makes

P0304 BMW
P0304 CHRYSLER
P0304 DODGE
P0304 JEEP
P0304 HONDA
P0304 ACURA
P0304 HYUNDAI
P0304 NISSAN
P0304 INFINITI
P0304 ISUZU
P0304 KIA
P0304 LEXUS
P0304 TOYOTA
P0304 SCION
P0304 MAZDA
P0304 MITSUBISHI
P0304 SUBARU
P0304 VOLKSWAGEN
P0304 AUDI
P0304 GMC
P0304 CHEVROLET
P0304 PONTIAC
P0304 FORD
P0304 BUICK
P0304 CADILLAC
P0304 SATURN
P0304 MERCURY
P0304 1999 MERCURY VILLAGER
P0304 VOLVO
P0304 HUMMER
P0304 JAGUAR