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Check Engine Light & Rough Idle on 2018 Countryman ALL4 - P0301/P0300

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Mike T. · rep 0 · May 25, 5:00 AM · 1 replies · solved · Question

Vehicle: 2018 Mini Cooper Countryman ALL4

My 2018 Mini Cooper Countryman ALL4 (F60), with about 55,000 miles, started running really rough yesterday. The check engine light came on, and it feels like it's misfiring, especially when I'm at a stoplight or idling.

I scanned it with my OBD-II reader and got codes P0301 (Cylinder 1 Misfire Detected) and P0300 (Random/Multiple Cylinder Misfire Detected). This is the first time I've had these issues. Could this be spark plugs or ignition coils? How difficult is it to replace these on this specific model, and is there anything else I should check before diving into parts replacement?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 5:00 AM

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ClearTheCode admin answer:

OBD-II codes P0301 and P0300 are classic indicators of an engine misfire, specifically pointing to Cylinder 1 and potentially other cylinders. This is a common maintenance item that can often be resolved with DIY effort.

Here’s a diagnostic and repair approach:

  1. Confirm the Codes: Re-scan to ensure the codes are consistent. Note any other codes present.
  2. Focus on Cylinder 1: Since P0301 is present, start by investigating components related to Cylinder 1.
  3. Inspect Spark Plug (Cylinder 1):
    • Locate Cylinder 1 (usually the one closest to the timing belt/chain side of the engine).
    • Carefully remove the ignition coil and then the spark plug. Inspect the plug for signs of wear, fouling (oil, carbon, fuel), or damage to the electrode.
    • DIY Tip: You can often swap the spark plug from Cylinder 1 with one from a known good cylinder (e.g., Cylinder 2). If the misfire moves to Cylinder 2 (P0302), you've identified a faulty spark plug.
  4. Inspect Ignition Coil (Cylinder 1):
    • Ignition coils are a very common failure point. Visually inspect the coil for cracks or signs of arcing.
    • DIY Tip: Similar to the spark plug, swap the ignition coil from Cylinder 1 with one from a known good cylinder. If the misfire moves to Cylinder 2 (P0302), the coil is the culprit.
  5. Consider All Spark Plugs/Coils: If your Mini is around 55,000 miles and spark plugs haven't been replaced, it's a good idea to replace all of them. If one coil is failing, others might not be far behind, so consider replacing all coils as well.
    • Tools: You'll typically need a spark plug socket (often a thin-walled 14mm or 16mm), a torque wrench, and possibly a coil puller tool.
  6. Other Potential Causes (if plugs/coils don't fix it):
    • Fuel Injector: A faulty fuel injector for Cylinder 1 could cause a misfire. This is harder to diagnose at home without specialized tools.
    • Compression Issue: Low compression in Cylinder 1 due to valve or piston ring issues. This would require a compression test.
    • Vacuum Leaks: Less likely to cause a specific cylinder misfire but can contribute to rough idle.

When to See a Shop:

  • If replacing spark plugs and coils doesn't resolve the misfire.
  • If you suspect a fuel injector or compression issue.
  • If the check engine light is flashing, indicating a severe misfire that could damage the catalytic converter.
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