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AutoCodes – Toyota – P0304 Toyota

P0304 Toyota Code - Cylinder 4 Misfire Detected

Quick Answer

When the engine misfires, high concentrations of Hydrocarbons (HC) enter the exhaust gas. Common causes include Intake air leak, Faulty spark plug #4, Faulty ignition coil #4. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0304 Toyota indicates Cylinder 4 Misfire Detected.
Common causes
Common causes include Intake air leak, Faulty spark plug #4, Faulty ignition coil #4.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
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Code Popularity 111,200
How popular is this code, among other codes? Medium
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Table of contents Created and updated by William Orellana on Aug 25, 2022
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Code P0304 Toyota Description

When the engine misfires, high concentrations of Hydrocarbons (HC) enter the exhaust gas. Extremely high hydrocarbon concentration levels can cause an increase in exhaust emission levels. Extremely high concentrations of hydrocarbons can also cause increases in the three-way catalytic converter temperature, which may cause damage to the three-way catalytic converter. To prevent this increase in emissions and to limit the possibility of thermal damage, the Engine Control Module (ECM) monitors the misfire count. When the temperature of the three-way catalytic converter reaches the point of thermal degradation, the ECM blinks the MIL. To monitor misfires, the ECM uses both the camshaft position sensor and the crankshaft position sensor. The camshaft position sensor is used to identify any misfiring cylinders and the crankshaft position sensor is used to measure variations in the crankshaft rotation speed. Misfires are counted when the crankshaft rotation speed variations exceed predetermined thresholds. If the misfire count exceeds the threshold levels and could cause emission control system performance deterioration, the ECM illuminates the MIL and stores a Diagnostic Trouble Code (DTC).
OBDII Code P0304 Toyota - Cylinder 4 Misfire Detected - AutoCodes.com
P0304 Toyota Code - Cylinder 4 Misfire Detected
What does this mean?

What are the Possible Causes of the DTC P0304 Toyota?

  • Intake air leak
  • Faulty spark plug #4
  • Faulty ignition coil #4
  • Clogged or faulty fuel injector #4
  • Fuel injectors #4 harness is open or shorted
  • Fuel Injectors #4 circuit poor electrical connection
  • Ignition coils #4 harness is open or shorted
  • Ignition coils #4 circuit poor electrical connection
  • Incorrect Fuel pressure
  • Faulty Mass Air Flow (MAF) Sensor
  • Faulty Engine Control Module (ECM)
  • Faulty Engine Coolant Temperature (ECT) Sensor

How to Fix the DTC P0304 Toyota?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

The P0304 code means that cylinder #4 is misfiring or is randomly misfiring. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder #4. If the problem persists more tests need to be done to diagnose the problem. See "Possible Causes" for the most common problems.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0304 Toyota code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0304 Toyota code?

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Information for Specific Toyota Models

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0304 Toyota Code

1. What are the common symptoms of OBDII code P0304 in a Toyota indicating a Cylinder 4 misfire?

- Common symptoms include rough idling, loss of power, engine vibrations, and potential fuel economy reduction.

2. What are the typical causes of a Cylinder 4 misfire in a Toyota triggering code P0304?

- Possible causes include faulty spark plugs, ignition coils, fuel injectors, vacuum leaks, low compression, or wiring issues.

3. How can I diagnose the Cylinder 4 misfire in a Toyota with OBDII code P0304?

- Diagnose by inspecting spark plugs, testing ignition coils, checking fuel injectors, performing a compression test, and scanning for other related trouble codes.

4. Can a bad fuel injector cause a Cylinder 4 misfire in a Toyota leading to code P0304?

- Yes, a faulty fuel injector can cause a misfire in Cylinder 4, leading to code P0304. Ensure to check and replace the injector if necessary.

5. What are some repair tips for addressing OBDII code P0304 related to a Cylinder 4 misfire in a Toyota?

- Replace spark plugs, ignition coils, or fuel injectors if faulty. Also, check for vacuum leaks, perform a compression test, and ensure proper wiring connections.

6. Will driving with OBDII code P0304 indicating a Cylinder 4 misfire in a Toyota cause further damage?

- Continued driving with a misfire can potentially damage the catalytic converter over time and may lead to more severe engine issues, so it's best to address the problem promptly.

7. How important is it to fix OBDII code P0304 associated with a Cylinder 4 misfire in a Toyota?

- It is crucial to address code P0304 promptly to prevent further engine damage, ensure optimal performance, and maintain fuel efficiency.

8. Can a simple fix like changing spark plugs resolve OBDII code P0304 in a Toyota due to a Cylinder 4 misfire?

- Yes, in some cases, a misfire related to code P0304 can be resolved by replacing worn-out spark plugs. However, it's recommended to perform a thorough diagnosis.

9. Are there any preventive measures to avoid OBDII code P0304 related to a Cylinder 4 misfire in a Toyota?

- Regular maintenance, such as changing spark plugs and inspecting ignition components, can help prevent misfires leading to code P0304 in the future.

10. How long does it typically take to repair OBDII code P0304 caused by a Cylinder 4 misfire in a Toyota?

- The repair time can vary based on the exact cause of the misfire. Simple fixes like changing spark plugs may take a short time, while more complex issues could require more extensive diagnostics and repairs.

Discuss the causes and fixes for P0304 Toyota OBDII Code

Submit a New Comment

  • 1999 Toyota Corolla P0304. I have changed the plug, Coil but Issue remain same. I also try to check the Injector and I could see that its working properly. Please what else need to be checked.

    Reply to Comment

  • Next step is to perform a compression test, you could have a blown head gasket.

    Reply to Comment

  • Thanks Tech - If its a blown head gasket, I think I would have probably be experiencing over heating

    Reply to Comment

  • No necessary, many times you could have a cylinder misfire without engine overheating. Actually we have one at our shop with the same problem.

    Reply to Comment
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