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2022 Canyon AT4 - Rough Idle and P0301/P0303 codes

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Mike T. · rep 0 · May 25, 2:35 AM · 1 replies · solved · Question

Vehicle: 2022 GMC Canyon AT4

Hi all,

My 2022 GMC Canyon AT4 (3.6L V6) recently started running really rough, especially when idling. It feels like the engine is shaking more than it should. The Check Engine Light came on, and when I scanned it, I got P0301 and P0303 codes. These are misfire codes for cylinders 1 and 3.

The truck only has about 30,000 miles on it, so I'm a bit surprised to see these issues already. What's the most likely culprit here, and what should I check first? I'm hoping it's something relatively simple.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:35 AM

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ClearTheCode admin answer:

The P0301 and P0303 codes indicate that your 2022 GMC Canyon AT4 is experiencing misfires in cylinders 1 and 3, respectively. A rough idle is a classic symptom of engine misfires. At 30,000 miles, this is relatively early for major component failure, suggesting it could be a simpler issue.

Here's a systematic approach to diagnose and resolve the misfires:

  1. Spark Plugs: While 30,000 miles is a bit early for spark plug replacement on many modern engines, a faulty or fouled plug can definitely cause a misfire. Given you have two specific cylinders misfiring, you can try swapping the spark plugs from cylinder 1 and 3 with known good cylinders (e.g., 2 and 4). If the misfire codes follow the plugs, you've found your issue.
  2. Ignition Coils: Each cylinder has its own ignition coil. A failing coil will prevent proper spark delivery. Similar to spark plugs, you can swap the ignition coils from cylinders 1 and 3 with other cylinders. If the misfire codes change to the new cylinder locations, the coils are the problem.
  3. Fuel Injectors: A clogged or faulty fuel injector for cylinders 1 and 3 would prevent adequate fuel delivery, causing a misfire. You can test injectors using a stethoscope to listen for their clicking sound, or by performing a fuel pressure drop test with a specialized tool. Swapping injectors is more involved but can also help diagnose.
  4. Vacuum Leaks: A vacuum leak near cylinders 1 and 3 could lean out the air/fuel mixture, causing misfires. Inspect vacuum lines, intake manifold gaskets, and PCV valve/hoses for cracks or disconnections.
  5. Compression Test: Although less likely at 30k miles, low compression in cylinders 1 and 3 due to valve issues, head gasket problems, or piston ring wear would cause misfires. This is a more advanced diagnostic step.

When to See a Shop:

If swapping spark plugs and ignition coils doesn't resolve the issue, or if you're not comfortable performing these checks yourself, it's time to take your Canyon to a qualified technician. They have advanced diagnostic tools that can:

  • Perform a cylinder power balance test to pinpoint the exact misfiring cylinder.
  • Conduct fuel injector pulse width and spray pattern tests.
  • Perform a professional compression and leak-down test.
  • Check for any related sensor issues (e.g., MAF, O2 sensors) that might indirectly contribute to misfires.
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