How To Fix P0304 Code in a Chevy? (Meaning, Cause, Symptoms, Diagnose)

P0304 Code chevy

Do you know how to fix the P0304 Code in a Chevy? this is one of the questions our readers ask a lot. Well, we´ve got you covered.

For most Americans, owning a functioning vehicle is a necessity to get to work, school, the grocery store, and more.

Consequently, if your Chevy has recently issued an OBDII error code P0304, you might be worried that your four-wheeled friend won’t get you much further.

Rest assured, though, Code P0304 is common and won’t lead to long-term damage as long as you get it fixed quickly.

Vehicle error code P0304 indicates that one of the cylinders in your vehicle is at fault. More often than not, though, code P0304 goes off when there are other issues that are causing your cylinders to misfire.

If left for too long, you’ll begin to feel the effects on your vehicle’s performance, which can eventually affect its overhaul drivability.

What does Code P0304 Mean in a Chevy Vehicle?

For all Chevy vehicles, Code P0304 indicates that the fourth cylinder in your vehicle is misfiring. By the fourth cylinder, we mean the fourth cylinder that fires—not the fourth visible cylinder.

Along with the warning code, you’ll also be able to tell if the fourth cylinder is misfiring because of the following symptoms:

  • Your Chevy will issue a check engine light
  • You’ll be able to feel strong vibrations at low RPMs
  • Your Chevy will not run as well
  • Your Chevy will eat up fuel
  • You may smell raw gasoline leaking from the exhaust
  • Your Chevy may begin backfiring

If the vibrations or overall performance become noticeably bad, take your Chevy to the nearest mechanic immediately.

How to Diagnose Code P0304 in a Chevy

A misfiring cylinder is typically caused by some other problem in the engine, not the cylinder itself. Before resetting the code, check the following parts for fault:

  • Bad spark plugs – Code P0304 is typically caused by bad spark plugs. Newer Chevy models are built using long-lasting iridium spark plugs but the plugs can still go bad over time. If your vehicle is running with bad plugs, the cylinders won’t get enough power to properly fire, leading to a P0304 code.
  • Faulty spark plug wires – If your Chevy’s spark plugs are fine, it could be the spark plug wires that are at fault. Without proper wiring, the electrical charge from your spark plugs will not reach the cylinders, causing them to misfire.
  • Broken fuel injector – It won’t be easy to diagnose a broken fuel injector but if your fuel injector has gone bad, it could be causing your cylinders to misfire. It’s less common than bad plugs and wires, though, so we don’t recommend starting here unless all of your cylinders are misfiring.
  • A leaking vacuum – If there’s a leak in your Chevy’s vacuum system, it could cause Cylinder 4 to misfire because your engine won’t get the proper mixture of fuel and air. If the problem is only affecting one cylinder, it’s likely because there’s a leak near the cylinder itself.
  • Bad sensors – It’s highly unlikely that your sensors are at fault but this is still one possible reason why your engine’s fourth cylinder isn’t firing properly. If your Chevy’s ECU isn’t receiving the correct signals from the cam or crank sensors, the cylinders will not fire in the right order.
  • Low Compression – Your Chevy could have a compression issue due to a bent valve, cracked head, leaky gasket, or some other larger problem. Without enough compression, the cylinders in your Chevy won’t completely fire, leading to a Code P0304.

Troubleshooting Code P0304 Misfire Detected Cylinder #4 Chevy Trailblazer >> Check out the video below:

How Bad is Code P0304?

If you don’t find and correct the problem, misfiring cylinders can lead to disastrous problems for your Chevy’s engine.

Therefore, you should inspect your vehicle and get it serviced as soon as possible. Misfiring cylinders can lead to long-term damage that could render your vehicle undrivable.

Simple issues such as bad plugs or wires are relatively cheap to fix—around $100-$200. More serious issues, such as a leaky vacuum or a broken fuel injector, will cost more to fix—up to $1,000.

How to Fix a Code P0304 on a Chevy Vehicle

Start by inspecting your vehicle for problems. You’ll have to find what’s causing the fourth cylinder to misfire before you can fix the code.

We recommend checking your spark plugs. Rotate them to see if the error code moves to another cylinder. If so, you’ve found the faulty plug and can easily replace it.

If the problem isn’t with your spark plugs or wires, you may need to take your vehicle to a trained mechanic.

After resolving the underlying issue, you can then reset the OBDII error code. If it comes back again, you may have more than one issue.


OBDII code P0304 means that your Chevy’s fourth cylinder is misfiring. It’s most likely because of faulty spark plugs or spark plug wires.

These problems are easy and cheap to fix but, if the problem is something larger—such as a leak in the vacuum system or damaged fuel injector—you could end up paying more.

We recommend having your vehicle services ASAP to prevent further damage.

Here are some of my favorite tools & equipment´s

Thank you for reading this article. I hope it helps you find the most recent and accurate technical and repair information for your car. Here are some tools that I use as an automotive technician and hope you´ll also find helpful.

There are affiliate links, so if you do decide to use any of them, I´ll earn a small commission. But in all honesty, these are the exact tools that I use and recommend to everyone, even my own family. (NO CRAP)

To see all my of most up-to-date recommendations, check out this resource that I made for you!



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.

Recent Posts

error: Content is protected !!