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2019 Canyon V6 Rough Idle & Misfire Codes - Spark Plugs/Coils?

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Mike T. · rep 0 · May 25, 2:40 AM · 1 replies · solved · Question

Vehicle: 2019 GMC Canyon SLT

Hey guys,

I've got a 2019 GMC Canyon SLT with the 3.6L V6 engine, currently sitting at about 78,000 miles. Lately, I've noticed a rough idle, especially when the engine is cold, and sometimes it feels like it's misfiring under light acceleration. The 'Check Engine' light came on, and when I scanned it, I got P0301 and P0303 codes, indicating misfires on cylinders 1 and 3.

I'm thinking it's probably time for new spark plugs, and maybe ignition coils too. Is this a common mileage for these components to go bad on the Canyon V6? What's the best approach to tackle this – just plugs, or should I do the coils as well? Any recommendations on specific brands or tips for the replacement process?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:40 AM

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ClearTheCode admin answer:

Experiencing rough idle and misfire codes (P0301, P0303) at 78,000 miles on your 2019 GMC Canyon 3.6L V6 is quite common, and your suspicion about spark plugs and ignition coils is likely correct. This mileage often falls within the range where these components start to show wear.

Causes & Diagnostics:

  1. Worn Spark Plugs: Over time, the electrodes on spark plugs erode, increasing the gap and requiring more voltage to fire. This leads to weak or inconsistent sparks, causing misfires.
  2. Failing Ignition Coils: Ignition coils provide the high voltage necessary for the spark plugs. They can degrade due to heat, vibration, or age, leading to intermittent or complete failure. A failing coil on a specific cylinder will cause a misfire on that cylinder.
  3. Other Potential Causes (Less Likely with P030x): Fuel injector issues, vacuum leaks, or low compression can also cause misfires, but the specific P030x codes often point directly to ignition system components.

DIY Maintenance Steps (Spark Plugs & Coils):

  1. Diagnosis Confirmation: Since you have P0301 and P0303, you can try swapping the ignition coils from cylinders 1 and 3 with coils from known good cylinders (e.g., 2 and 4). If the misfire codes follow the coils (e.g., you now get P0302 and P0304), then the coils are the issue. If the codes remain P0301 and P0303, then the spark plugs are the more likely culprit.
  2. Spark Plugs: For your 3.6L V6, the spark plugs are typically located under the ignition coils on top of the engine. You'll need to remove the engine cover, disconnect the electrical connectors from the coils, and unbolt the coils to access the plugs. Use a spark plug socket with a rubber insert to prevent damage to the porcelain.
  3. Ignition Coils: It's generally recommended to replace all spark plugs at once. For ignition coils, if one or two have failed, it's often a good idea to replace all of them, as others may not be far behind. Use OEM or high-quality aftermarket coils.
  4. Gap & Torque: Ensure new spark plugs are pre-gapped correctly (check your owner's manual or plug specifications) and torque them to the manufacturer's specifications to avoid damage.

When to See a Shop:

  • Persistent Misfires: If replacing plugs and coils doesn't resolve the issue, or if new codes appear, a professional diagnosis is needed. They can perform advanced tests like compression checks, fuel pressure tests, or injector pulse tests.
  • Difficulty Accessing: Some spark plugs, especially on V6 engines, can be challenging to access due to intake manifold placement or tight spaces. If you're uncomfortable, a shop can handle it efficiently.
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