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2021 GLE 350 Check Engine Light - P0171 & P0174 Codes

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Paul Z. · rep 0 · May 22, 4:16 AM · 1 replies · solved · Question

Vehicle: 2021 Mercedes-Benz GLE 350

My 2021 Mercedes-Benz GLE 350 (V167) recently threw a Check Engine Light, and when I scanned it, I got codes P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2). The car seems to be running okay, maybe a slight hesitation sometimes, but nothing major. Fuel economy might be a little worse.

I'm wondering what the most common causes for these lean codes are on a relatively new Mercedes. Could it be O2 sensors already, or something else like a vacuum leak? Any advice on where to start looking before I take it to the dealer?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:16 AM

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ClearTheCode admin answer:

Codes P0171 and P0174, indicating a 'System Too Lean' condition on both Bank 1 and Bank 2, suggest that the engine's air-fuel mixture is consistently running with too much air or not enough fuel. Since both banks are affected, it points to a problem common to the entire engine, rather than just one side.

Common Causes for P0171/P0174 on a 2021 GLE 350:

  1. Vacuum Leaks: This is a very common cause. Leaks in vacuum lines, intake manifold gaskets, PCV system components, or brake booster hoses can introduce unmetered air into the engine.
  2. Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can incorrectly report the amount of air entering the engine, leading the ECU to inject less fuel than needed.
  3. Fuel Delivery Issues: While less common on newer vehicles, a failing fuel pump, clogged fuel filter, or faulty fuel pressure regulator could lead to insufficient fuel delivery to both banks.
  4. Exhaust Leaks: Leaks before the oxygen sensors can allow ambient air to enter the exhaust stream, tricking the O2 sensors into reporting a lean condition.
  5. Oxygen (O2) Sensors: While possible, it's less likely for both upstream O2 sensors (pre-catalytic converter) to fail simultaneously on a 2021 model. However, a single faulty sensor could potentially skew readings if it's a shared component.

Troubleshooting Steps:

  1. Visual Inspection for Vacuum Leaks: Carefully inspect all visible vacuum lines, the intake manifold area, and the PCV valve for any cracks, disconnections, or signs of leaks.
  2. Clean MAF Sensor: Disconnect the MAF sensor and carefully clean it with specialized MAF sensor cleaner. Do NOT use other cleaners.
  3. Check Air Filter: Ensure the engine air filter is clean and properly seated.

When to See a Shop:

If the basic checks don't resolve the issue, it's best to take your 2021 GLE 350 to a Mercedes-Benz dealership or a reputable independent shop. They have advanced diagnostic tools that can monitor live data from the O2 sensors, fuel trims, and MAF sensor. This data is crucial for accurately diagnosing the root cause. They can also perform smoke tests to pinpoint elusive vacuum leaks or conduct fuel pressure tests. Addressing lean conditions promptly is important, as prolonged operation can lead to reduced engine performance, increased emissions, and potential damage to catalytic converters over time.

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