2018 Sorento V6 - Check Engine Light with P0301 and rough idle after fill-up

ClearTheCode admin answer: A P0301 code indicates a misfire on cylinder 1. While it can sometimes be related to fuel quality, it's more often an issue with the ignition or fuel delivery system for that specific cylinder.

Here's a diagnostic approach:

1. Check Spark Plug and Ignition Coil: The most common causes for a P0301 are a faulty spark plug or ignition coil for cylinder 1. If you're comfortable, you can inspect the spark plug for wear or fouling. You could also try swapping the ignition coil from cylinder 1 with a coil from a different cylinder (e.g., cylinder 3) and see if the misfire code moves (e.g., to P0303). If it does, the coil is the culprit.
2. Fuel Injector Check: A clogged or faulty fuel injector for cylinder 1 can also cause a misfire. This is harder to diagnose without specialized tools, but a fuel system cleaner might offer a temporary solution if it's a minor clog.
3. Vacuum Leaks: Less common for a single-cylinder misfire, but a vacuum leak near cylinder 1 could lean out the mixture enough to cause a misfire. Listen for hissing sounds around the intake manifold.
4. Compression Test: If the above steps don't resolve the issue, a compression test on cylinder 1 would be the next step to rule out internal engine problems like a bad valve or head gasket, though this is less likely with a P0301 alone.

When to See a Shop:

• If swapping coils doesn't move the misfire, or if you're not comfortable performing these diagnostic steps yourself.
• If the misfire is severe, causing significant shaking or a flashing check engine light (which indicates a severe misfire that could damage the catalytic converter).
• If the problem persists after checking/replacing the spark plug and coil.
• If you suspect a fuel injector or internal engine issue, as these require more advanced diagnostics and tools.