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2020 Altima 2.5 S rough idle and P0301 code after fill-up

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Mike T. · rep 0 · May 25, 1:54 AM · 1 replies · solved · Question

Vehicle: 2020 Nissan Altima 2.5 S

My 2020 Nissan Altima 2.5 S (about 45,000 miles) started running really rough after I filled up with gas yesterday. The engine is shaking noticeably at idle, and I can feel a slight loss of power when accelerating. The Check Engine Light came on, and I scanned it with my OBD-II reader.

It's showing a P0301 code, which points to a misfire in cylinder 1. I'm wondering if it's bad gas, or something else entirely. Could it be a spark plug, coil pack, or something more serious? Any ideas on where to start troubleshooting this?

I've only ever used regular unleaded. This is the first time I've had any engine issues with this car.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:54 AM

0

ClearTheCode admin answer:

A P0301 code specifically indicates a misfire detected in cylinder 1. While bad fuel can sometimes contribute, it's more likely to be an issue with one of the components responsible for the combustion process in that specific cylinder.

Possible Causes for P0301:

  1. Failing Spark Plug: A worn, fouled, or damaged spark plug in cylinder 1 is a very common cause of misfires.
  2. Faulty Ignition Coil: The ignition coil provides the high voltage to the spark plug. If the coil for cylinder 1 is weak or failed, it won't ignite the fuel properly.
  3. Clogged or Failing Fuel Injector: A fuel injector that isn't delivering the correct amount of fuel to cylinder 1 (either too much or too little) can cause a misfire.
  4. Vacuum Leak: A vacuum leak near cylinder 1 could lean out the air/fuel mixture, leading to a misfire.
  5. Low Compression: Less common, but internal engine issues like a bad valve or piston ring in cylinder 1 can result in low compression and a misfire.

When to See a Shop:

  • Promptly: While you can attempt some basic troubleshooting, driving with a persistent misfire can lead to unburnt fuel entering the exhaust system, potentially damaging your catalytic converter, which is an expensive repair.

Diagnostics & Troubleshooting Steps:

  1. Inspect Spark Plug & Coil: If you're comfortable, you can visually inspect the spark plug and ignition coil for cylinder 1. Look for cracks, corrosion, or signs of oil fouling on the spark plug. You can also try swapping the coil pack from cylinder 1 with another cylinder (e.g., cylinder 2). If the misfire code moves to cylinder 2 (P0302), you've identified a bad coil pack.
  2. Fuel Quality Check: While less likely to be the sole cause of a single-cylinder misfire, ensure you've used the correct octane fuel. If you suspect bad gas, you might consider adding a fuel system cleaner.
  3. Professional Diagnosis: A shop can perform more advanced diagnostics, including:
    • Fuel Pressure Test: To check the fuel delivery system.
    • Injector Pulse Test: To verify the fuel injector for cylinder 1 is firing correctly.
    • Compression Test: To check the internal health of cylinder 1.
    • Smoke Test: To identify any vacuum leaks.
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