How To Fix P0304 Code For Toyota Vehicles (Meaning, Causes, Symptoms, Diagnosis, Cost of Repair)

P0304 Code Toyota

Do you know how to fix the P0304 code for Toyota vehicles (Camry, 4Runner, Corolla, Prius, Tacoma, Sienna, Tundra, or Rva4)? this is one of the questions our readers ask a lot. Well, we´ve got you covered.

Every Toyota owner wants to ensure the pristine health and condition of their vehicle. However, it can sometimes be difficult to discern engine troubles based on codes.

If your Toyota receives a P0304 code, then you’ll need to look into issues with misfiring cylinders in your car. In this guide, we’ll look at the best way to go about fixing a P0304 code on a Toyota vehicle.

First, we’ll discuss the root of this issue and its meaning for your vehicle’s health. Then, we’ll look at the main symptoms of a P0304 code, as well as how to get it diagnosed. Finally, we can estimate the cost of repairing this cylinder-based issue. Read on to learn the specifics.

Meaning of P0304 Code For Toyota

If you receive the auto code P0304 on your Toyota vehicle, your first thought is likely to wonder what this code means.

The first thing to note is that a P0304 is a common code indicating an engine misfire in Toyotas. It’s pretty common in Corolla models specifically, where it indicates a misfire in cylinder 4. 

Engine misfires are a serious cause for concern with any vehicle you drive, Toyotas included. Therefore, if you get a P0304 code on your car, you should look into fixing the issue immediately.

At worst, this issue could lead to a ruined engine if left unfixed. It’s also dangerous to drive with a misfiring cylinder in your engine. 

This issue could cause your vehicle to lose power while driving, or worse – cause your car to break down on the road. 

Read also: How to Fix a P0401 Code on Mitsubishi (Step by Step)

Causes of the P0304 Code on Toyota

While the cause for a P0304 code (misfiring cylinder) isn’t always the same, there are some common factors that create this issue.

Misfiring cylinders aren’t always caused by a malfunction in the cylinder itself. This problem can also occur due to issues with related parts in the vehicle’s engine. 

For example, you could have issues with the vehicle’s ignition coil, such as a shorted harness or a bad electrical connection in the circuit.

Or, you might have similar malfunctions with the fuel injector related to the misfiring cylinder. 

Other causes of the code P0304 include malfunctioning spark plugs, clogged fuel injectors, an intake air leak, bad fuel pressure (issues with fuel pressure sensor), or poor cylinder compression.

The good thing to note is that you can detect all of these issues and diagnose them if you look at the symptoms your car is displaying.

Symptoms of the P0304 Code

One of the most obvious symptoms a Toyota will display when the P0304 code issue occurs is a light indicating a need to service the engine.

However, there are several other symptoms that indicate a misfiring cylinder that has to do with the performance of your vehicle. 

Namely, you may notice that your gas mileage starts to become lower than what it usually is. Or, your car may begin to show signs of bad performance, like vibrating or making noises when running because of rough running.

More evident signs, however, include engine backfiring, excretions of fuel from the tailpipe, loss of electrical power, or hard engine starts.

You should pay close attention to any of these symptoms, and don’t hesitate to get the problem diagnosed.

Diagnosis of the P0304 Code For Toyota

Symptoms can give you an idea of the diagnosis of your problem when you get a P0304 code on your Toyota. However, it’s advisable to go to an auto shop to get a professional diagnosis.

There are several typical diagnoses related to this code, and we’ll share the ways they get diagnosed.

One diagnosis you may get is a “low compression” diagnosis. You can arrive at this diagnosis if your engine has issues with its gasket, valve, or other parts.

Or, you might have a diagnosis of a “bad fuel injector”. 

Other diagnoses include:

  • “Bad coil pack” – diagnosed by testing the engine’s coil packs
  • “Faulty spark plugs” – diagnosed by looking at the electrodes (bad plugs damage the electrodes)
  • “Faulty spark plug wires” – diagnosed by a mechanic in most cases

How to repair engine error failure code P0304 Toyota Corolla >> Check out the video below:

Estimated Cost of Repair

The cost of repair associated with a code P0304 on a Toyota Corolla will vary depending on the diagnosis you receive.

However, we can look at the individual diagnoses and share estimates of repairing/replacing those faulty parts.

  • Coil Replacement – costs $280 on average
  • Spark Plug Wire Replacement – costs $150 on average
  • Fuel Injector Replacement – costs $940 on average
  • Spark Plug Replacement – costs $135 on average
  • Head Gasket Replacement – costs $1700 on average
  • Valve Replacement – costs $1300 on average


A P0304 code on a Toyota vehicle (Camry, 4Runner, Corolla, Prius, Tacoma, Sienna, Tundra or Rva4) is indicative of a serious issue within the engine – a misfiring cylinder.

This is typically related to cylinder 4 in a Toyota Corolla, and the cost to fix this issue varies depending on the diagnosis.

Always get a proper diagnosis and aim to fix this issue quickly, as it can be dangerous to drive with this code.

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Jeff is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Reatta. Jeff has been creating written and video content about transportation, automotive, electric cars, future vehicles as well as new, used for more than 18 years. Jeff is based in Boulder, Colorado.

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