P0304 Engine Code: Causes, Symptoms and Fix

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 a number of auto sensors and parts that operate together harmoniously for a smooth operation.

Misfiring is one of the obvious problems that a car’s engine might experience. Almost anyone can recognize it.

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

What is Error P0304 Code?

The P0304 error is usually logged by the PCM when a misfire is been detected in the engine. A misfire often occurs when the engine combustion is compromised in any of the cylinders – the no.4 cylinder in the case of P0304 3 engine code.

According to the information obtained from the crankshaft position sensor, the PCM or engine control module (ECM), logs the misfire error code. Any broken cylinder will cause the crankshaft rotational speed to decrease as the internal combustion cycles.

The PCM will issue a corresponding error code and illuminate the check engine light on the dashboard.

A P0304 engine code simply means cylinder 4 misfire detected.

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.

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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 the signal received from the PCM to the driver.

2. Engine Hard start

The P0304 is often accompanied by difficulties while trying to start the vehicle. This is due to a faulty or dead cylinder.

3. Excess gas usage

If your vehicle starts consuming excess fuel then it could be as a result of the presence of Error P0304 code.

Although, don’t jump to conclusions yet since there are other codes that 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 them escape from the tailpipe and app increasing 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 4 fuel injector
  6. Problematic Camshaft and Crankshaft Sensor
  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
  • Replacing the distributor cap, coil packs, and/or spark plug wires.
  • Vacuum leaks repaired
  • Addressing fuel delivery problems
  • Fixing internal mechanical issues.
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How serious is the P0304 Engine Code?

A P0304 error is a critical problem that needs to be fixed right away. This typically occurs when the engine management unit notices unburned fuel in the fourth cylinder.

The catalytic converter is prone to becoming fouled or clogged by unburned gasoline if the issue isn’t addressed on time.

Which could eventually lead to failure on other connected components. As a result, you should identify the issue’s primary cause and resolve it as quickly as you can.


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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