What Does Engine Code P0304 Mean?

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If your car is displaying a P0304 engine code, it has detected a cylinder 4 misfire. There could be a number of causes and it may mean there is something wrong with your ignition system or fuel system—or it could be an internal engine failure. This is a serious issue that requires prompt servicing.
Diagnostic trouble codes (DTC) are designed to identify an issue with a car’s engine. Car owners should understand what these engine codes mean. This way, you’ll be able to determine the severity of the issue and how quickly you need to get it fixed.
Car insurance comparison and broker app Jerry can make you a more informed driver by protecting your car with valuable information on DTCs and meaningful savings on your car insurance. In this article, we’re exploring the P0420 engine code: what problem is it indicating, what you should do when it shows, and the costs to fix it. 
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What does the engine code P0304 mean?

Definition: Cylinder 4 misfire detected
The P0304 engine code analyzes information from the crankshaft position sensor and the camshaft position sensor to indicate that an engine cylinder is misfiring
Cylinders are vital components of a car engine. They are the chambers where fuel combusts and power generates that allow a car to operate.

How much will it cost to fix?

The diagnostic cost is about one hour of labor. The hourly cost varies per auto shop and depends on the make and model of the car.
Most auto shops charge between $75 and $150 per hour.

What can cause the P0304 engine code?

The P0304 engine code can be caused by several things, all of which can be serious and require immediate attention. Ultimately, a cylinder misfire can damage your car engine and result in costlier repairs if left unattended. 
The main issue caused by misfiring cylinders is damage to the catalytic converter. The catalytic converter’s purpose is an important one as it converts toxic gases and pollutants into less toxic pollutants through the process of catalyzing a redox reaction.
The common causes behind the P0304 engine code include:
  • Faulty spark plug 4
  • Clogged or faulty fuel injector 4
  • Faulty ignition coil 4
  • Fuel injector 4 circuit poor electrical connection
  • Ignition coil 4 harness is open or shorted
  • Ignition coil 4 circuit poor electrical connection
  • Insufficient cylinder 4 compression
  • Incorrect fuel pressure
  • Intake air leak

Common symptoms of the P0304 engine code

A P0304 engine code can have a host of symptoms. Many of these symptoms will not be visible to the untrained eye, but here are some to look out for:
  • Engine light on
  • Lack or loss of power
  • Hard start
  • Engine hesitation
If any of these happen after the P0304 engine code shows, they are most likely related.

How serious is the P0304 engine code?

The P0304 engine code is rather serious as it is indicating an extreme cylinder misfire, which can result in damage to your catalytic converter and harm your engine. 
Once the engine control module (ECM) detects one or more cylinder misfiring, the DTC that monitors that respective cylinder will activate and one or two of the corresponding fuel injectors will be disabled for at least 30 seconds
If the misfire is still present after the fuel injector has been enabled and after producing 200 engine revolutions, the ECM will again disable the fuel injector. If a fuel injector fault DTC happens during a misfire, the injector will remain disabled.
Since vital parts of your engine can be compromised from this misfire, it is considered very serious and should be fixed right away.

Can I fix the P0304 engine code myself?

Yes, if you know what you’re doing then you can perform the repairs yourself. Here’s what you’ll need to do:
  • Visually inspect the related wiring harness and connectors
  • Look for any damaged components, specifically looking for broken, pushed out, bent, or corroded connector’s pins
  • To fix the problem, you will most likely have to replace the spark plugs on cylinder 4
If this doesn’t fix it, then you should conduct more tests to try to pinpoint the problem.

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