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2017 Yukon XL Hard Starting and Fuel Smell - P0171/P0174

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Mike T. · rep 0 · May 25, 2:36 AM · 1 replies · solved · Question

Vehicle: 2017 GMC Yukon XL SLT

Hello everyone,

I own a 2017 GMC Yukon XL SLT with the 5.3L V8 engine, and I've been having some intermittent issues that are really starting to bother me. The main problem is that it's often hard to start, especially after it's been sitting for a while. It cranks for a few seconds longer than it should before finally firing up. Sometimes, it feels like it's going to stall right after starting.

Adding to that, I've noticed a faint but distinct smell of fuel around the vehicle, particularly when it's just been driven. The check engine light has also come on a couple of times, giving me P0171 and P0174 codes, which are for System Too Lean (Bank 1 and Bank 2). I'm worried about a fuel leak or a failing fuel pump. Has anyone experienced these symptoms with their Yukon? What should I be looking for?

I'm hoping it's something relatively simple, but the fuel smell and the lean codes together are making me nervous. Any guidance would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:36 AM

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ClearTheCode admin answer:

The combination of hard starting, a fuel smell, and P0171/P0174 codes (System Too Lean on both banks) in your 2017 GMC Yukon XL points towards a few common areas within the fuel and vacuum systems. Here's a breakdown:

  1. Vacuum Leaks:

    • Cause: The most common cause of lean codes on both banks is a large vacuum leak, often from the intake manifold gasket, PCV system, or other vacuum hoses. This allows unmetered air into the engine, leaning out the air/fuel mixture.
    • Diagnostics: Visually inspect all vacuum lines for cracks, disconnections, or deterioration. Pay close attention to the PCV valve and its hoses, as well as the intake manifold area. A smoke test performed by a mechanic is the most effective way to find subtle vacuum leaks.

  2. Fuel Pump/Fuel Pressure Regulator:

    • Cause: A failing fuel pump may not deliver adequate fuel pressure, leading to hard starting and a lean condition. A faulty fuel pressure regulator can also cause similar issues by not maintaining proper pressure.
    • Diagnostics: A fuel pressure test is crucial. A mechanic can connect a gauge to the fuel rail to check if the pressure is within specifications, both at idle and under load. Low pressure would indicate a failing pump or a clogged fuel filter (though less common on newer models with in-tank filters).

  3. Fuel Injector Issues:

    • Cause: While less likely to cause lean codes on both banks simultaneously unless multiple injectors are failing, clogged or leaking injectors can contribute to hard starts and lean conditions.
    • Diagnostics: A fuel injector balance test can help identify faulty injectors, but this is usually performed after other common issues are ruled out.

  4. EVAP System Leaks (related to fuel smell):

    • Cause: The fuel smell, especially if it's intermittent, could indicate a leak in the Evaporative Emission Control (EVAP) system. This system captures fuel vapors to prevent them from escaping into the atmosphere. A leak here won't directly cause lean codes but can be a separate issue.
    • Diagnostics: Check the fuel cap for proper sealing. A smoke test of the EVAP system can pinpoint leaks in lines, the charcoal canister, or the purge/vent solenoids. OBD codes like P0440, P0442, or P0455 would typically accompany EVAP leaks.

When to See a Shop:

  • Immediately if the fuel smell becomes strong or persistent, as this could indicate a fire hazard.
  • If you cannot locate any obvious vacuum leaks after a thorough visual inspection.
  • If the hard starting becomes more frequent or leads to stalling.
  • For a proper fuel pressure test and EVAP system diagnostics, as these require specialized tools and expertise.
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