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2020 Civic Sport Rough Idle and Misfire Codes P0301, P0303

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Mike T. · rep 0 · May 22, 2:41 AM · 1 replies · solved · Question

Vehicle: 2020 Honda Civic Sport

Hi all,

My 2020 Honda Civic Sport (1.5T engine) has developed a really rough idle lately. It feels like it's shaking more than usual when stopped at a light. The check engine light came on, and when I scanned it, I got P0301 and P0303, indicating misfires in cylinders 1 and 3.

I've read that spark plugs or ignition coils are common culprits for misfires. The car has about 60,000 miles on it, and I haven't changed the plugs yet. Could this be the issue, or should I be looking at something else?

Any specific advice for the 1.5T engine in the Civic? Thanks for your help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 2:41 AM

0

ClearTheCode admin answer:

Experiencing a rough idle and misfire codes (P0301, P0303) on your 2020 Honda Civic Sport at 60,000 miles is a common diagnostic scenario. Here's how to approach it:

  1. Confirm Misfire Codes: The P030x codes (P0301 for cylinder 1, P0303 for cylinder 3) directly point to misfires in those specific cylinders. This is a good starting point.
  2. Common Causes for Misfires:
    • Ignition System: This is the most frequent cause.
      • Spark Plugs: At 60,000 miles, your spark plugs are due for inspection or replacement, especially if they're the original ones. Worn plugs can lead to weak spark.
      • Ignition Coils: A failing ignition coil for cylinder 1 or 3 would directly cause a misfire. You can often swap coils between cylinders (e.g., move coil from cylinder 1 to cylinder 2) to see if the misfire code follows the coil. If P0302 appears after the swap, the coil is bad.
    • Fuel System:
      • Fuel Injectors: A clogged or faulty fuel injector in cylinder 1 or 3 could prevent proper fuel delivery.
      • Low Fuel Pressure: Less common for specific cylinder misfires, but overall low fuel pressure can affect multiple cylinders.
    • Compression Issues:
      • Low Compression: Issues like worn piston rings, valve problems, or a blown head gasket can cause low compression in a cylinder, leading to a misfire. This is less common but more serious.
  3. Recommended Diagnostic Steps:
    • Inspect/Replace Spark Plugs: Given your mileage, start here. Replace all four spark plugs with OEM-equivalent parts.
    • Test Ignition Coils: If new plugs don't resolve it, try swapping the ignition coils as described above.
    • Check Fuel Injectors: If coils and plugs are good, a shop can test fuel injector resistance and spray patterns.

When to See a Shop:

  • If replacing spark plugs and testing coils doesn't resolve the issue.
  • If you suspect fuel injector problems or more serious internal engine issues (compression test needed).
  • If the check engine light is flashing, indicating a severe misfire that could damage the catalytic converter.
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