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DTC P0304 in a Toyota vehicle indicates a misfire in cylinder 4. This code can be triggered by various issues related to the ignition system, fuel system, or engine mechanical problems. Here’s a detailed explanation of the code, its causes, symptoms, and potential solutions:

Meaning of DTC P0304
Code: P0304
Description: Cylinder 4 Misfire Detected
Potential Causes
Faulty Spark Plug:

The spark plug in cylinder 4 may be worn, fouled, or damaged.
Faulty Ignition Coil:

The ignition coil for cylinder 4 may be malfunctioning or failing.
Fuel Injector Issues:

The fuel injector for cylinder 4 may be clogged, dirty, or faulty.
Vacuum Leaks:

A vacuum leak near cylinder 4 can cause a misfire.
Compression Issues:

Low compression in cylinder 4 due to worn piston rings, damaged valves, or a blown head gasket.
Fuel System Problems:

Issues with the fuel pump or fuel pressure regulator affecting the delivery of fuel to cylinder 4.
Wiring Issues:

Damaged or corroded wiring or connectors related to the ignition coil or fuel injector in cylinder 4.
Engine Control Module (ECM) Issues:

Rarely, the ECM may be malfunctioning and causing a misfire.
Symptoms
Check Engine Light (CEL) illuminated
Rough idling
Engine hesitation or stalling
Poor acceleration
Reduced engine performance
Increased fuel consumption
Noticeable engine vibrations
Diagnostic and Repair Steps
Scan for Additional Codes:

Use an OBD-II scanner to check for any additional trouble codes that might provide more insight into the issue.
Inspect and Test the Spark Plug:

Remove and inspect the spark plug from cylinder 4. Check for signs of wear, fouling, or damage.
Replace the spark plug if necessary.
Test the Ignition Coil:

Swap the ignition coil from cylinder 4 with another cylinder to see if the misfire moves.
If the misfire moves to the other cylinder, replace the faulty ignition coil.
Inspect and Clean the Fuel Injector:

Use a fuel injector cleaner or have the injectors professionally cleaned.
Swap the fuel injector from cylinder 4 with another cylinder to see if the misfire moves.
Replace the fuel injector if necessary.
Check for Vacuum Leaks:

Inspect the vacuum lines near cylinder 4 for any signs of leaks or disconnections.
Repair any leaks found.
Perform a Compression Test:

Conduct a compression test on all cylinders to check for low compression in cylinder 4.
If compression is low, further diagnose to determine if the issue is with the piston rings, valves, or head gasket.
Inspect the Fuel System:

Ensure the fuel pump and fuel pressure regulator are delivering the correct fuel pressure.
Repair or replace any faulty fuel system components.
Check Wiring and Connectors:

Inspect the wiring and connectors for the ignition coil and fuel injector in cylinder 4 for any signs of damage or corrosion.
Repair or replace any damaged wiring or connectors.
Clear the Code and Test:

After performing the necessary repairs, use an OBD-II scanner to clear the code.
Test drive the vehicle to ensure the problem is resolved and the code does not return.
Professional Help
If you’re unable to diagnose or fix the issue yourself, it’s recommended to seek help from a certified Toyota technician. They will have the necessary tools and expertise to properly diagnose and repair the problem.

Addressing DTC P0304 promptly is important to ensure your vehicle’s engine performs efficiently and reliably, preventing further issues and ensuring safe operation.

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