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2018 XC90 T6 - Check Engine Light with P0302 and rough idle

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Chris P. · rep 0 · May 22, 5:09 AM · 1 replies · solved · Question

Vehicle: 2018 Volvo XC90 T6 Momentum

Hey everyone,

My 2018 Volvo XC90 T6, with about 75,000 miles, just threw a Check Engine Light this morning. It's also running pretty rough, especially at idle, and I can feel a slight hesitation when accelerating.

I hooked up my OBD-II scanner and it's showing a P0302 code, which points to a misfire on cylinder 2. I'm wondering if anyone else has experienced this with their XC90 and what the common culprits might be. Could it be a bad spark plug, ignition coil, or something more serious?

Any advice on troubleshooting steps before I take it to the shop would be greatly appreciated. Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:09 AM

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ClearTheCode admin answer:

A P0302 code indicates a misfire detected in cylinder 2. This is a common diagnostic code, and several components can cause it. Here's a breakdown of potential causes and troubleshooting steps:

  1. Spark Plug: The most common and easiest fix. A worn or fouled spark plug in cylinder 2 can cause a misfire. Inspect the plug for damage, excessive wear, or carbon buildup. If it's been a while since your last spark plug replacement, this is a good starting point.
  2. Ignition Coil: Each cylinder has its own ignition coil. A failing coil for cylinder 2 would prevent proper spark. You can often test this by swapping the coil from cylinder 2 with an adjacent cylinder (e.g., cylinder 1 or 3). If the misfire code moves to the new cylinder, the coil is faulty.
  3. Fuel Injector: A clogged or faulty fuel injector for cylinder 2 can lead to an insufficient fuel supply, causing a misfire. This is harder to diagnose without specialized tools but can be indicated by fuel trim readings.
  4. Compression Issue: Less common, but a loss of compression in cylinder 2 (due to a bad valve, head gasket, or piston ring) will cause a misfire. This requires a compression test.
  5. Vacuum Leaks: While less likely to cause a single-cylinder misfire, significant vacuum leaks can affect engine performance and sometimes trigger misfires.

When to See a Shop:

  • If swapping the ignition coil doesn't move the misfire, and replacing the spark plug doesn't resolve the issue.
  • If you suspect a fuel injector problem or a compression issue, as these require more advanced diagnostic tools and expertise.
  • If the rough idle is severe, or the vehicle is in 'limp mode,' it's best to have it professionally diagnosed to prevent further engine damage.

Driving with a persistent misfire can damage your catalytic converter due to unburnt fuel entering the exhaust system. Address this issue promptly.

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