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2020 Camry SE Check Engine Light and Rough Idle - P0304 Code

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Mike T. · rep 0 · May 25, 1:24 AM · 1 replies · solved · Question

Vehicle: 2020 Toyota Camry SE

Hey everyone,

My 2020 Toyota Camry SE, with about 65,000 miles, just threw a Check Engine Light this morning. It also started running a bit rough, especially at idle. It feels like there's a slight shake coming from the engine compartment.

I hooked up my OBD-II scanner and pulled a P0304 code, which indicates a misfire on cylinder 4. I haven't done any major work on it recently, just routine oil changes and tire rotations.

Any ideas on what might be causing this? Is this something I can tackle myself, or should I take it straight to the shop? I'm hoping it's not too serious.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:24 AM

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ClearTheCode admin answer:

A P0304 code indicates a misfire in cylinder 4. This is a common diagnostic code and can stem from several issues. Addressing it promptly is important to prevent potential damage to your catalytic converter.

Here's a breakdown of common causes and diagnostic steps:

  1. Spark Plugs: A worn or fouled spark plug in cylinder 4 is a very common culprit. Spark plugs typically need replacement every 60,000-100,000 miles, depending on your vehicle's maintenance schedule.
  2. Ignition Coil: The ignition coil for cylinder 4 could be failing. You can often diagnose this by swapping the coil from cylinder 4 with a coil from a different cylinder (e.g., cylinder 1). If the misfire code moves to the new cylinder (e.g., P0301), then you've identified a faulty coil.
  3. Fuel Injector: A clogged or faulty fuel injector for cylinder 4 would prevent proper fuel delivery, leading to a misfire. This is less common than spark plug or coil issues but definitely possible.
  4. Compression Issues: In more severe cases, a misfire can indicate low compression in the cylinder, possibly due to a worn piston ring, valve issue, or head gasket problem. This usually requires more in-depth diagnostics.
  5. Vacuum Leaks: While less direct for a single cylinder misfire, a significant vacuum leak could potentially affect engine operation and contribute to misfires.

When to see a shop:

  • If swapping the ignition coil doesn't move the misfire, or if you're uncomfortable performing these diagnostic steps yourself.
  • If the misfire is accompanied by other symptoms like excessive smoke from the exhaust, significant power loss, or unusual engine noises.
  • If you suspect a fuel injector issue or low compression, as these require specialized tools and expertise to diagnose and repair effectively.

For a P0304, start by checking the spark plug and ignition coil for cylinder 4. These are often DIY-friendly repairs.

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