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2023 Yukon Denali Rough Idle and Check Engine Light - Fuel System?

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Rachel A. · rep 0 · May 22, 3:38 AM · 1 replies · solved · Question

Vehicle: 2023 GMC Yukon Denali

Hello forum,

I'm experiencing some concerning issues with my 2023 GMC Yukon Denali, which has the 6.2L V8 engine and only about 15,000 miles on it. Lately, I've noticed a rough idle, especially when the engine is warm, and sometimes it feels like it's stumbling a bit at low speeds. The check engine light has come on intermittently, and I'm a bit stumped.

When I checked the codes, I'm getting P0171 (System Too Lean Bank 1) and sometimes P0300 (Random/Multiple Cylinder Misfire Detected). I've heard about direct injection engines having carbon buildup issues, even at lower mileage, or potential fuel pump problems. I'm running premium fuel as recommended.

Has anyone with a newer 2023 Yukon or similar GMC experienced these lean codes and rough idle? What was the cause, and what should I be looking for? Any advice before I take it to the dealer?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:38 AM

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ClearTheCode admin answer:

Experiencing a rough idle, P0171 (System Too Lean Bank 1), and P0300 (Random Misfire) on your 2023 GMC Yukon Denali with the 6.2L V8 at only 15,000 miles points towards a fuel or air delivery issue, which needs prompt attention.

Common Causes for Lean Conditions and Misfires:

  1. Vacuum Leaks: Even a small vacuum leak on Bank 1 (P0171) can introduce unmetered air, causing a lean condition and rough idle.
  2. Fuel System Issues:
    • Low Fuel Pressure: A failing high-pressure fuel pump (HPFP) or low-pressure fuel pump (LPFP) can lead to insufficient fuel delivery.
    • Clogged Fuel Injectors: Direct injection injectors can become partially clogged, especially if fuel quality is inconsistent, leading to a lean condition in specific cylinders.
    • Fuel Filter: While less common at low mileage, a restricted fuel filter could contribute.
  3. Oxygen Sensor Malfunction: A faulty O2 sensor on Bank 1 could be providing incorrect readings, though it's usually a symptom rather than the cause of a lean condition.
  4. MAF Sensor Issues: A dirty or faulty MAF sensor can incorrectly report air intake, leading the ECM to deliver too little fuel.
  5. Spark Plugs/Coil Packs: While less likely to cause a lean code, faulty spark plugs or ignition coils can cause misfires (P0300).

Diagnostics & Next Steps:

  1. Check for Vacuum Leaks: Visually inspect all vacuum lines and intake manifold gaskets. A smoke test can definitively find leaks.
  2. Fuel Pressure Test: A shop can test both low-pressure and high-pressure fuel system pressures to ensure they are within specifications.
  3. Fuel Injector Testing: Specialized equipment can test injector spray patterns and flow rates.
  4. Live Data Monitoring: A professional scan tool can monitor O2 sensor readings, fuel trims, and MAF sensor data to identify anomalies.

When to See a Shop:

Given the low mileage and the nature of these codes, it's best to take your Yukon Denali to a GMC dealership immediately. Since it's a newer vehicle, it's likely still under warranty, and they have the specialized diagnostic tools and technical bulletins for these specific engines. Driving with a persistent lean condition can lead to engine damage, including catalytic converter failure, due to excessive heat and improper combustion.

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