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All codes/P0304

P0304

Cylinder 4 Misfire Detected

High severity

Your engine's computer has detected that cylinder number 4 is not firing correctly, meaning it's not contributing power as it should.

The powertrain control module (PCM) has detected a misfire condition in cylinder number 4.

Common causes

  • Faulty Spark Plug (Cylinder 4)

    A worn, fouled, or damaged spark plug in cylinder 4 is a very common cause of a single-cylinder misfire.

    high

    Typical part cost: $10-30

  • Faulty Ignition Coil or Wire (Cylinder 4)

    A failing ignition coil or damaged spark plug wire specific to cylinder 4 will prevent proper spark delivery.

    high

    Typical part cost: $50-200

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First things to check

  1. 1Swap spark plug from cylinder 4 to another cylinder and see if the misfire moves.
  2. 2Swap ignition coil from cylinder 4 to another cylinder and see if the misfire moves.

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Tools you may need

Already have a compatible scanner? Use it. If not, a Bluetooth OBD2 adapter can help you confirm engine codes and check supported live sensor data before replacing parts.

Illustration of a Bluetooth OBD2 adapter, not a product photo

Basic checks

Veepeak OBDCheck BLE

A Bluetooth LE adapter for reading standard engine codes and supported live data.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Regular diagnostics

vgate iCar Pro BLE 4.0

A Bluetooth LE adapter with an automatic sleep feature for routine code and sensor checks.

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Illustration of a Bluetooth OBD2 adapter, not a product photo

Another option

OBDLink CX

A Bluetooth LE adapter to consider when comparing supported vehicles and diagnostic apps.

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Illustrations shown, not product photos. Check vehicle, phone and app compatibility before buying. These adapters do not guarantee access to ABS, airbags or manufacturer-specific systems. Clearing a code does not repair the fault and can reset emissions readiness monitors.

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Related codes

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Frequently asked questions

What's the most common fix for a P0304?

The most common and often easiest fix is replacing the spark plug and/or ignition coil for cylinder 4. These components are wear items and frequently fail, leading to misfires.

Can a P0304 code be caused by a bad mass air flow (MAF) sensor?

While a bad MAF sensor can cause general engine performance issues and sometimes P0300 (multiple misfires) due to incorrect air measurement, it's less likely to cause a misfire specifically in cylinder 4 unless there's an additional, localized problem.

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