how to fix P0304 misfire code in my Toyota Corolla E140 (2006-2013)

Toyota Corolla E140 (2006-2013)

Error Codes

2-4 hours

Time

medium

Difficulty

high

Severity

Error Code: P0304

4 min read

631 words

⚠️ Safety Warning

This issue requires immediate attention. If you are not experienced with automotive repairs, consult a professional mechanic. Working on critical systems can be dangerous.

Problem Statement

Learn how to diagnose and fix P0304 cylinder 4 misfire in Toyota Corolla. Step-by-step guide with diagnostic procedures and repair instructions.

Error Code

P0304

Affected Component

Engine

Estimated Time

2-4 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical components.
•Allow the engine to cool before opening any components to prevent burns.

Symptoms

•Check engine light illuminated
•Rough idle, especially at low RPMs
•Decreased fuel economy
•Engine stalling or hesitation during acceleration
•Increased exhaust emissions
•Possible engine vibration

Diagnostic Steps

1
Scan the vehicle using an OBD-II scanner to confirm the P0304 code and check for any additional codes.
2
Inspect the spark plug in cylinder 4 for wear, damage, or carbon buildup.
3
Check the ignition coil for cylinder 4 for proper operation and signs of arcing or damage.
4
Perform a compression test on cylinder 4 to ensure it has appropriate compression levels.
5
Inspect the fuel injector for cylinder 4 for clogs or electrical issues.
6
Examine vacuum hoses and intake manifold gaskets for leaks that could affect cylinder performance.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•OBD-II scanner
•Socket set
•Torque wrench
•Spark plug socket
•Compression gauge
•Fuel injector cleaning kit (if needed)
•Multimeter

Parts Required

•Spark plug (cylinder 4)
•Ignition coil (cylinder 4)
•Fuel injector (if faulty)

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Diagnostic Steps

1
Scan the vehicle using an OBD-II scanner to confirm the P0304 code and check for any additional codes.
2
Inspect the spark plug in cylinder 4 for wear, damage, or carbon buildup.
3
Check the ignition coil for cylinder 4 for proper operation and signs of arcing or damage.
4
Perform a compression test on cylinder 4 to ensure it has appropriate compression levels.
5
Inspect the fuel injector for cylinder 4 for clogs or electrical issues.
6
Examine vacuum hoses and intake manifold gaskets for leaks that could affect cylinder performance.

Solution

1. Preparation

Gather necessary tools and parts.
Disconnect the battery to prevent electrical shorts.
Allow the engine to cool before working on it.

2. Replace Spark Plug

Tools Required: Socket set, torque wrench, spark plug socket.
Remove the ignition coil from cylinder 4 by unscrewing the bolts and disconnecting the electrical connector.
Use a spark plug socket to remove the old spark plug from cylinder 4.
Inspect the old spark plug for signs of wear; replace it if necessary with a new one that meets OEM specifications (usually around 0.044 inches gap).
Install the new spark plug by hand to avoid cross-threading, then torque to the manufacturer's specification (typically around 13 lb-ft).

3. Replace Ignition Coil

Tools Required: Socket set, torque wrench.
After removing the ignition coil, inspect the connector for corrosion.
Install the new ignition coil onto the spark plug and secure it with bolts; torque to manufacturer specifications (usually around 8 lb-ft).
Reconnect the electrical connector to the ignition coil.

4. Inspect and Clean Fuel Injector

Tools Required: Fuel injector cleaning kit (if needed), multimeter.
Disconnect the electrical connector from the fuel injector for cylinder 4.
Use a multimeter to test the injector’s resistance; replace if out of specification.
Clean the injector using a fuel injector cleaning kit or replace it with a new one if necessary.

5. Compression Test

Tools Required: Compression gauge.
Reconnect the ignition coil and spark plug temporarily.
Remove the fuel pump fuse to prevent fuel delivery.
Crank the engine and take the compression reading.
If compression is low, further investigation into valve issues or head gasket failure may be required.