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CEL with P0171 & P0174 on my 2020 Genesis G80 - Rough Idle

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Ryan M. · rep 0 · May 22, 6:12 AM · 1 replies · solved · Question

Vehicle: 2020 Genesis G80 3.8L Advanced

Hey everyone,

I'm hoping someone can help me out. My Check Engine Light came on a few days ago in my 2020 Genesis G80 3.8L Advanced. I noticed a bit of a rough idle, especially when I'm stopped at a light, and sometimes a slight hesitation when accelerating from a stop.

I took it to AutoZone to get the codes read, and it's showing P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2). Both banks being lean has me a bit worried.

Has anyone experienced this with their G80 or another Genesis model? What should I be looking for first? I'm trying to avoid a huge dealership bill if it's something I can check myself. Any advice would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 6:12 AM

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ClearTheCode admin answer:

The P0171 and P0174 codes indicate that your engine's computer (ECM) is detecting a 'System Too Lean' condition on both Bank 1 and Bank 2. This means there's either too much air or not enough fuel in the combustion mixture. Since both banks are affected, it often points to a common issue rather than a problem specific to one side of the engine.

Here are the common causes and troubleshooting steps:

  1. Vacuum Leaks: This is the most frequent culprit for both lean codes.
    • Causes: Leaks in the intake manifold gasket, PCV valve and hoses, brake booster hose, or other vacuum lines.
    • Troubleshooting: Listen for a hissing sound around the engine bay. Visually inspect all vacuum hoses for cracks or disconnections. A professional smoke test can pinpoint hard-to-find leaks.
  2. Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect air volume readings to the ECM.
    • Causes: Contamination from an old air filter or oil from an aftermarket oiled air filter.
    • Troubleshooting: Carefully clean the MAF sensor with a dedicated MAF sensor cleaner (do NOT use brake cleaner or other harsh chemicals).
  3. Fuel System Issues:
    • Causes: Low fuel pressure (due to a failing fuel pump or clogged fuel filter), or partially clogged fuel injectors. While less common for both banks simultaneously, a weak fuel pump could affect overall pressure.
    • Troubleshooting: Checking fuel pressure requires specialized tools and is best left to a professional.
  4. Exhaust Leaks: Leaks in the exhaust system before the oxygen sensors can draw in ambient air, causing the O2 sensors to report a lean condition.
    • Causes: Cracked exhaust manifold, loose exhaust pipe connections.
    • Troubleshooting: Visually inspect the exhaust manifold and pipes for soot stains or cracks.

When to see a shop: If you've checked for obvious vacuum leaks and cleaned your MAF sensor without success, it's time to consult a qualified technician. They have diagnostic tools to monitor live data (like fuel trims and O2 sensor readings), perform a fuel pressure test, and conduct a smoke test to accurately diagnose the root cause. Driving with a persistent lean condition can lead to long-term engine damage, including catalytic converter failure.

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