Toyota Corolla Check Engine Light – Spark Plug Issues?

The misfire codes P0301 through P0304 refer to misfires in cylinders 1 through 4 in your Toyota Corolla, which could indeed be caused by worn-out spark plugs. Here are a few steps and recommendations for addressing the issue:
1. Check the Spark Plugs

Worn-out spark plugs are a common cause of misfires, especially if they havent been replaced in a while. Its a good idea to inspect and replace the spark plugs if they appear worn, fouled, o r damaged.
OEM Spark Plugs are generally recommended for your Corolla because they provide the best fit and performance. Brands like NGK o r Denso both are often used in Toyotas are good options for OEM replacements.
If you’re considering aftermarket spark plugs, be sure to choose ones that are specifically designed for your Corolla model to avoid compatibility issues.

2. Check the Ignition Coils

Misfires can also occur if the ignition coils are faulty. While it’s not always necessary to replace them along with the spark plugs, it might be worth checking the coils for any signs of wear o r damage. If you notice issues with the ignition coils, o r if they are the original ones, it might be a good idea to replace them to prevent further misfires.
If you have the resources, it can be helpful to swap ignition coils between cylinders to see if the misfire code follows the coil. This can help determine if a coil is faulty.

3. Other Potential Causes

Wiring issues: Damaged o r loose wires can cause misfires. Make sure the wiring to the ignition system is intact.
Fuel injectors: If the spark plugs and coils seem fine, the misfire could be related to fuel delivery, such as clogged o r faulty injectors. In this case, you may need to clean o r replace the injectors.

4. Perform a Diagnostic Test

If you’re unsure whether the spark plugs o r coils are the cause, performing a thorough diagnostic test o r taking the car to a mechanic could help pinpoint the issue.

5. Changing the Spark Plugs and Coils

Replacing the spark plugs is a relatively easy DIY job if you have the proper tools, but if you’re not comfortable with the process, it’s worth taking your Corolla to a mechanic.
If you decide to replace the ignition coils, be sure to check if they’re due for replacement, especially if they’re the original coils.