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P0304 Engine Code: Causes, Symptoms and Fix

February 23, 2024 | Victor Lukasso

A P0304 Engine Code is an OBD-II error code that denotes that the PCM (Powertrain control module)has recorded a misfire in cylinder 4.

An engine is a precisely tuned machine with several auto sensors and parts that operate together to ensure better compression and performance. Still, misfiring can occur along the states of using your engine, and it’s often associated with the error P0304 error code.

When an engine misfires, gas is not properly burned in the engine, causing the car to slow down due to the cylinders being unable to combust appropriately.

Nevertheless, let’s see the causes, symptoms, and how to fix the P0304 error code.


What is Error P0304 Code?

The error P0304 emphasizes misfiring, which implies that a cylinder – in this context – fails to work in the correct sequence. Since a cylinder comprises various combustion chambers, the PCM usually logs the P0304 when detecting a misfire on the 4th cylinder.

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The PCM, or engine control module, saves the misfire error code before forwarding it to the crankshaft position sensor, reducing the internal combustion rate due to the faulty cylinder.

You’ll see the error P0304 code illuminate on your check engine light to inform you that a misfire has been noticed on cylinder no.4.

Without wasting much time, here are some symptoms associated with the P0304 Misfiring code.

Symptoms of P0304 Engine Code

While the P0304 engine code will affect cars differently depending on the model, here are some signs and symptoms to watch out for in your vehicle.

1. illuminated check engine light

This will probably be the first sign to watch out for if your vehicle runs into the p0304 engine trouble. The check engine light will turn on to pass across the signal received from the PCM to the driver.

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2. Engine Hard start

The P0304 is often accompanied by difficulties while trying to start the vehicle. This is due to a broken 4th cylinder.

3. Excess gas consumption

Your vehicle’s gas consumption will increase if you ever run into a P0304 code because the gas won’t be burnt appropriately when it reaches the 4th cylinder, increasing fuel mileage.

Although, don’t jump to conclusions yet since other codes are accompanied by poor gas mileage.

3. Rough Idle

4. Stalling while idle

5. Engine Loss of Power

6. Gas smell due to unburnt fuel

A faulty cylinder will leave most fuel unburnt, making it escape from the tailpipe and increase fuel usage.

7. Poor Acceleration

Causes of P0304 Engine Code

These are some renowned causes of the P0304 error code on your vehicle

  1. Problematic Spark Plugs
  2. Damaged distributor rotor
  3. Vacuum leaks
  4. Faulty spark plug wires
  5. Faulty cylinder four fuel injector
  6. Problematic Camshaft and Crankshaft Sensors
  7. Low Engine Compression
  8. Leaking Head Gasket

How to Fix P0304 Engine Code

If you’re looking for how to Fix the P0304 error code on your vehicle Once and for all, implement any of the following fixes:

  • Spark plug maintenance or replacement
  • The distributor cap, coil packs, and spark plug wires are replaced.
  • Vacuum leaks repaired
  • Addressing fuel delivery problems
  • Fixing internal mechanical issues.
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How serious is the P0304 Engine Code?

The P0304 engine code is a critical trouble that needs instant diagnosis and fixing to prevent increased fuel mileage, misfiring, and stalling of your engine; the error code mainly arises due to a broken cylinder in the 4th chamber.

This results in fuel unburned when they reach the fourth cylinder, which will cause further damage to the catalytic convert since it will likely get clogged or folded by unburnt gasoline. The result is that other engine components become unresponsive.

So, it’s best to identify and eliminate the p0304 error code as soon as possible.


Everything you need to know about a P0304 engine misfire, including its causes, symptoms, and tracking down and fixing it, has been covered on this page.

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Meet Victor Lukasso, the owner of V. Auto Basics. Through this blog, Victor Provides Insights on the latest tips, maintenance, repair, and techniques in the automotive world.