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Check Engine Light P0171/P0174 on 2018 Ram 1500 Hemi – Lean Codes

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Angela R. · rep 0 · May 22, 3:34 AM · 1 replies · solved · Question

Vehicle: 2018 Ram 1500 Laramie

My 2018 Ram 1500 Laramie with the 5.7L Hemi just threw a Check Engine Light, and when I scanned it, I got codes P0171 and P0174 – System Too Lean (Bank 1 and Bank 2). The truck seems to be running okay, maybe a slight rough idle sometimes, but nothing major. Fuel economy might be a little worse.

What are the most common causes for both banks to run lean on these Hemi engines? I'm hoping it's something relatively simple like a sensor or a vacuum leak, and not something more serious. Any advice on where to start looking?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:34 AM

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ClearTheCode admin answer:

Diagnostic Trouble Codes P0171 and P0174 indicate that the engine's air-fuel mixture is too lean on both banks. This means there's too much air or not enough fuel. Since both banks are affected, it points to a common issue rather than a single O2 sensor or injector.

  1. Vacuum Leaks: This is one of the most common causes for lean codes on both banks. Inspect all vacuum lines, the PCV valve and hose, intake manifold gaskets, and the brake booster hose for cracks or disconnections. A smoke test can effectively pinpoint these leaks.
  2. Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect air mass readings to the PCM, leading it to inject less fuel than needed. Try cleaning the MAF sensor with a specialized MAF sensor cleaner (do not use other solvents).
  3. Fuel Delivery Issues:
    • Weak Fuel Pump: A failing fuel pump may not be delivering adequate fuel pressure to the engine.
    • Clogged Fuel Filter: While less common on newer Rams with in-tank filters, a restricted filter can reduce fuel flow.
    • Clogged Fuel Injectors: Though less likely to affect all injectors evenly, partially clogged injectors can contribute to a lean condition.
  4. Exhaust Leaks: Leaks before the upstream oxygen sensors can draw in ambient air, tricking the O2 sensors into reading a lean condition and causing the PCM to over-fuel, which is counter-intuitive but can happen.
  5. Faulty O2 Sensors: While less likely to be both at once, a failing upstream O2 sensor on each bank could theoretically cause this. However, common causes are usually upstream of the sensors.

When to See a Shop:

  • If you've checked for obvious vacuum leaks and cleaned the MAF sensor without success.
  • If you suspect fuel pressure issues, as this requires specialized tools to test.
  • A professional can perform a comprehensive diagnostic, including live data monitoring of fuel trims, O2 sensor readings, and fuel pressure, to accurately pinpoint the root cause. They can also check for other related DTCs that might not be immediately apparent.
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