Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
Your car's engine has a problem with one of its parts called Cylinder 4. It's not working right, and this can make the car shake or not run smoothly.
The engine control module (ECM) has detected that cylinder 4 is not firing properly, which can cause performance issues.
The P0304 code indicates that the engine control module has detected a misfire in cylinder 4. A misfire occurs when the air-fuel mixture in the cylinder fails to ignite properly, which can lead to rough engine performance and increased emissions.
• Check Engine Light is on
• Engine runs rough
• Decrease in fuel efficiency
• Engine shaking or vibrating
• Loss of power
• Faulty spark plug in cylinder 4
• Defective ignition coil
• Fuel injector issue in cylinder 4
• Vacuum leak
• Low engine compression
Cylinder: A chamber in the engine where fuel is burned to produce power.
Misfire: A failure of the air-fuel mixture in the engine cylinder to ignite properly.
• Use an OBD-II scanner to confirm the P0304 code.
• Inspect the spark plug in cylinder 4 for wear or damage.
• Test the ignition coil for proper operation.
• Check the fuel injector for cylinder 4.
• Perform a compression test on cylinder 4.
• Replace the spark plug in cylinder 4.
• Replace the ignition coil if faulty.
• Clean or replace the fuel injector for cylinder 4.
• Repair any vacuum leaks.
• Address any compression issues.
• OBD-II scanner
• Spark plug socket
• Multimeter
• Compression tester
• Fuel injector cleaner
$150 - $500
Moderate
• Toyota Camry
• Honda Accord
• Ford F-150
• Regularly replace spark plugs.
• Perform routine engine maintenance.
• Use quality fuel.
Engine Performance
• Do not ignore the Check Engine Light.
• Have the vehicle inspected by a professional if unsure.
• Avoid driving the car if it feels unsafe.
Check with the vehicle manufacturer for specific warranty coverage on engine components.
Misfire codes like P0304 have been common since the introduction of OBD-II systems in the mid-1990s, often related to ignition system issues.
Moderate – While the car may still be drivable, ignoring the issue can lead to more severe engine damage.
Driving with a misfire can increase emissions and may be illegal in areas with strict emissions regulations.
• Engine at operating temperature
• Vehicle at idle or under load
Cylinder 4 is typically located on the engine block, and its position can vary depending on the engine configuration.
Q: Can I drive my car with a P0304 code?
A: It's possible, but not recommended as it can cause further damage to the engine.
Q: How can I prevent a cylinder misfire?
A: Regular maintenance such as changing spark plugs and using quality fuel can help prevent misfires.
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Fitment Required · Vehicle-fitment part
Commonly relevant for misfire, ignition-efficiency, and some drivability-related repairs.
Misfire and ignition-related faults commonly involve spark plugs as part of the repair path.
Check the correct plug type, gap, and engine application for your vehicle.
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Fitment Required · Vehicle-fitment part
Relevant when the fault points toward ignition-coil performance or cylinder-specific ignition issues.
Some ignition faults involve coil performance or cylinder-specific coil problems.
Match the coil to your engine and confirm the failed component before ordering.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.