P0304 Trouble Code: Meaning, Symptoms, Causes, & Fixes

The proper combustion of the air-fuel mixture is very important for the efficient working of the engine. When your air-fuel mixture doesn’t burn properly, your engine starts misfiring. A misfire can be easily noticed by retrieving the activation code from the car’s onboard diagnostics system. These trouble codes represent particular conditions and are generally related to the affected cylinder(s). The diagnostic trouble code (DTC) P0304 represents a misfiring in cylinder 4. This article mainly explains the P0304 code symptoms, causes, and fixing costs.

P0304 Code Definition

P0304 code stands for “Cylinder 4 Misfire Detected.”

What Does the P0304 Code Mean?

The P0304 code indicates that your powertrain control module (PCM) has detected that cylinder 4 is not firing properly.

P0304 Code

Vehicles run on the combustion of an air-fuel mixture, which generates power in combustion chambers. The combustion chamber is also called a cylinder. A vehicle engine usually contains 4, 6, or 8 cylinders.

As you increase the number of cylinders, your engine power will be increased. A piston moves upward and downward inside the cylinder at a specific time. Misfires generally occur when this ignition timing is off.

Your PCM continuously records the working of all engine cylinders to ensure all cylinders are firing properly. Whenever any of these cylinders start misfiring, PCM triggers a code, and your check engine light starts flashing. The P0304 trouble code indicates that your vehicle engine cylinder number 4 is misfiring.

Anything from the bad spark plug to low engine compression may cause the misfires. Therefore, as your vehicle engine starts misfiring, you should travel your car to the nearest workshop to fix the main issue. You shouldn’t ignore misfiring because it may cause engine damage or complete failure of the engine.

Causes of P0304 Code

  • Faulty crankshaft sensor
  • Bad camshaft sensor
  • Low fuel pressure
  • Bad spark plugs
  • Vacuum leak
  • Damaged wiring of the spark plug
  • Bad ignition coils
  • Engine timing off
  • Faulty oil distributor
  • Head gasket leaks
  • Faulty fuel pressure sensor
  • Bad air-fuel ratio sensor
  • Faulty fuel injector 
  • Contaminated fuel
  • Low engine compression
  • A damaged lifter or worn camshaft lobe 

Symptoms of P0304 Code

  • Check Engine Light illumination
  • Jerking/Hesitations when driving
  • The gas smell from the exhaust pipe
  • Misfires
  • A reduction in the engine power
  • Poor fuel economy
  • Rough idle
  • Engine stalling

Read More: P0193 Code Symptoms and Causes

How to Diagnose the P0304 Code?

You need the following tools to diagnose or fix the P0304 code:

  • Screwdrivers
  • Digital Multimeter
  • Pliers
  • Spark plug wires
  • OBD-II scan tool
  • Spark plugs
  • Leakdown tester
  • Socket, ratchet, and extension
  • Compression tester
  • Fuel pressure gauge
  • Plug spanner

Follow the below-given steps to diagnose the P0304 code:

  • Use an OBD-II scan tool to check the presence of the P0304 code
  • Record all stored fault codes, along with all available freeze frame data. Clear the codes and make a test drive. If the code returns, then move forward for further inspection.
  • Inspect for loose connectors at the ignition coils
  • Inspect the wires for damage (especially cylinder 4).
  • Inspect the loose engine ground wiring.
  • Visually inspect the spark plugs and spark plug wiring. If your car has individual packs other than the spark plug wires, first remove the coil from cylinder #4 and replace it with the coil of cylinder #1. Now check; if your engine misfiring is due to cylinder #1 (P0301), it means the coil pack is defective, and you should replace it. The same test can be done for the spark plugs of cylinder #4, i.e., moving spark plugs from cylinder #4 to cylinder #2, and if the misfire is P0302, it means your spark plug is bad. If necessary, replace the spark plug and spark plug wiring and again check for the misfire.
  • If your ignition system is working efficiently, there may be an issue within the fuel system. For this, inspect the components of the fuel system, such as the fuel injector, fuel pump, fuel regulator, and fuel pressure sensor. You must also check the fuel level and fuel pressure. This is because low fuel pressure may lead the irregular misfires on multiple cylinders.
  • After the fuel system and ignition system inspection, perform a compression test and leak-down test to check if there are any engine mechanical issues causing the misfire. The mechanical parts (such as worn valve guides, head gasket leak, damaged valve, bad piston ring, or damaged valve spring) may cause the engine to misfire.

Common P0304 Code Diagnosing Mistakes

  • Not properly inspecting all the parts
  • Replacing the unnecessary components
  • Inability to confirm the presence of the P0304 code.
  • Clearing the code without first verifying the problem
  • Not clearing the PCM codes after fixing the codes

How serious is the P0304 Code?

DTC P0304 is usually considered a serious problem. You shouldn’t ignore this code and fix it as soon as possible. This is because spark-related misfires can allow unburned fuel to enter the exhaust pipe, where it can superheat. This superheated fuel has the ability to damage the catalytic converter, eventually leading to failure.

In any case, the root cause of the P0304 trouble code must be diagnosed and addressed quickly. This avoids unplanned downtime and unnecessary repair costs.

Repair Cost of P0304 Code

After diagnosing, the P0304 code may need one or more of the following repairs to fix the original problem.

Spark Plug replacement$60 to $260
Spark plug wiring repair$170 to $250
Fuel injector replacement$1400 to $2000
Ignition Coils$220 to $650
Fuel pump replacement$250 to $1,090

FAQ Section

Can I drive with the P0304 Code?

P0304 doesn’t stop your car from being driven to a safe location once symptoms start. This code indicates a misfire. A misfire indicates the engine’s internal problems.

If you continue driving with misfiring, it may badly damage your engine. Misfire also generates different drivability issues, such as poor fuel economy, poor acceleration, or a reduction in engine power. Therefore, you shouldn’t drive your vehicle with this code for a long time.

What repairs can fix the P0304 code?

  • Replacing the bad spark plugs
  • Replacing the bad fuel injectors
  • Replacing the bad fuel pumps
  • Adding more fuel if needed
  • Replacing the spark plug wiring or coil pack
  • Replacing the fuel pressure sensor
  • Replacing the fuel regulator
  • Repairing the fuel rail leaks
  • Fixing air leaks
  • Reprograming or replacing the PCM

Can a misfire fix itself?

No, the engine misfire can’t fix itself. It indicates a serious issue with your engine. However, if you don’t fix it on time and continuously ignore it, it may cause the complete failure of the engine.

How do I fix a cylinder misfire?

  • Inspecting the fuel pressure and fuel level. Add more fuel if the fuel level is less than a specific level.
  • Replace the fuel pump.
  • Replace the fuel injector.
  • Replace the fuel filter.
  • Replace the fuel pressure sensor.
  • Replace the spark plug.

Can a misfire damage your engine?

If left untreated, a cylinder misfire can lead to significant engine damage. Worse, if you experience a bad misfire while driving, it could result in an accident. This is why it’s important to treat engine misfires as soon as you detect them.

What is the symptom of error code P0304?

  1. Check Engine Light illumination
  2. Jerking/Hesitations when driving
  3. Fuel smell from the exhaust pipe
  4. Misfires
  5. A reduction in the engine power
  6. Poor fuel economy
  7. Rough idle
  8. Engine stalling
Read More
  1. Code P0191 Symptoms and Causes
  2. Code P2096 Meaning, Symptoms, and Causes
  3. P02196 Meaning, Symptoms, and Causes
  4. P2270 Meaning, Symptoms, and Causes
  5. P0153 Code Symptoms and Causes

Leave a Comment