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Generic gasoline powertrain DTC / Combustion and misfire monitoring

P0304: Cylinder 4 misfire detected

The controller detected misfire activity associated with cylinder 4.

Generic definition
P0300
P0303
P0204

Likely cause paths · unconfirmed

A possible ignition, fuel, or mechanical misfire

The controller detected uneven combustion, but the code does not identify the failed part or prove an ignition fault.

  • Record flashing versus steady warning-lamp behavior.
  • Note whether the symptom occurs at idle, acceleration, or both.

A possible engine condition affecting multiple cylinders

Air/fuel correction, compression, wiring, or another engine condition can cause or contribute to misfire activity.

  • Save companion codes and freeze-frame.
  • Do not continue driving to reproduce severe shaking.

Likely causes and repair directions are general, conditional orientation. The SAE citation supports the generic DTC definition only; it does not validate these causes, tests, repairs, or fitment to a particular vehicle.

Conditional likely repairs

A code describes a monitored condition; it does not prove a failed part. Use these directions only after confirming the cause.

If confirmed: A possible ignition, fuel, or mechanical misfire

If cylinder testing confirms an ignition, fuel, or mechanical cause, repair that confirmed cause using vehicle-specific service information.

Evidence to confirm

  • Misfire counters or tests identify a repeatable cylinder/pattern.
  • The relevant ignition, fuel, or mechanical test confirms the fault before parts are selected.

If confirmed: A possible engine condition affecting multiple cylinders

If testing identifies an air/fuel or shared engine cause, correct that verified condition and confirm misfire activity is resolved.

Evidence to confirm

  • Scan data and an appropriate leak, signal, fuel, or mechanical test point to the same cause.
  • Misfire monitoring is reassessed after the confirmed repair.

Guided evidence checks

  1. 01

    Record what happened

    Note when the warning appeared, what the vehicle was doing, and any recent service or change. Do not deliberately recreate an unsafe symptom.

  2. 02

    Make only a safe visual check

    Note whether the check-engine light is steady or flashing and when shaking occurs. Do not road-test a vehicle that feels unsafe.

  3. 03

    Preserve scan-tool evidence

    Qualified technician

    Save current/pending codes, freeze-frame, and available misfire counters before clearing anything.

  4. 04

    Confirm the system path

    Qualified technician

    A qualified technician should use cylinder-specific ignition, fuel, and mechanical tests; cylinder numbering is engine-specific.

Code-specific symptom note

  • Code-specific symptoms are not verified by the cited definition. Record the driver’s actual observations separately.

This generic code reference is not an OEM procedure, does not confirm that a DTC applies to a particular make/model/engine, and is not a repair diagnosis. Follow vehicle-specific service information or consult a qualified technician.