Troubleshooting P0171 and P0174
(Ford 4.6L, 5.4L)

Troubleshooting P0171 and P0174 (Ford 4.6L, 5.4L)

This article will help you to diagnose diagnostic trouble code P0171 (System too Lean Bank 1) and/or P0174 (System too Lean Bank 2) on your Ford, Mercury or Lincoln 4.6L or 5.4L equipped car, pick up, van or SUV.

Although you can apply this info to any Ford vehicle with a V6 or V8, this info concentrates on the Ford 4.6L and 5.4L V8 engines.

Here are the contents of this tutorial at a glance:

  1. Important Suggestions and Tips.
  2. P0171 and P0174 Essentials.
  3. Where are Bank 1 and Bank 2?.
  4. TEST 1: Fuel Trim Check.
  5. TEST 2: Inducing a Rich Condition.
  6. Other Important P0171 and P0174 Tests.
  7. Low Fuel Pressure Causing a Lean Condition.
  8. Checking for Vacuum Leaks with Carb Spray.
  9. Most Common Causes of P0171, P0174 DTC's.
  10. I've Done all of the Tests and I Still Have Codes P0171, P0174.
  11. More Ford 4.6L, 5.4L Diagnostic Tutorials.

Important Suggestions and Tips

Tip 1: You'll need a scan tool (that has Live Data capability) to take advantage of my tips and suggestions in this article.

Now, having said that, I've geared this article towards the person that owns a generic scan tool with Live Data capability (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool). You don't need to have a professional technician level scan tool (the scan tool in my photos is just a generic scan tool with Live Data).

Tip 2: Some of my testing suggestions involve tests with the engine running, this means you've got to be on your toes and alert. Think safety all of the time.

P0171 and P0174 Essentials

P0171: System Too Lean Bank 1.

  1. PCM's Adaptive Fuel Strategy has reached its rich calibrated limit for bank 1.
  2. In plain English, this means that the PCM has detected a vacuum leak (it may be real or perceived) and is compensating by injecting the maximum amount allowed (under its program) of fuel into the cylinders for bank 1.

P0174: System Too Lean Bank 2.

  1. PCM's Adaptive Fuel Strategy has reached its rich calibrated limit for bank 2.
  2. In plain English, this means that the PCM has detected a vacuum leak (it may be real or perceived) and is compensating by injecting the maximum amount allowed (under its program) of fuel into the cylinders for bank 2.

The very first thing you need to know, about these two diagnostic trouble code (DTC), is that they do not accuse anything specific as being BAD. In other words, they are only describing a condition in which the Computer is seeing an unmetered amount of air entering the engine, that no matter how much fuel it dumps (into the engine), it can not compensate for it.

This unmetered air entering the engine is usually due to a very large vacuum leak... but not always and this is what complicates things a bit. Several things can fool the PCM into thinking there is a vacuum leak, like a failing oxygen sensor or even a very dirty MAF sensor.

And so, the bottom line is that several different things and conditions can cause these diagnostic trouble code to pop up and light up the check engine light (CEL) on your Ford pick up or SUV.

In this article, I'm gonna' explore several of the things and conditions that cause a lean condition. More importantly, I'll offer you a diagnostic strategy that will help you to troubleshoot the issue.

Where are Bank 1 and Bank 2?

You may be wondering where Bank 1 and Bank 2 are located on your Ford 4.6L/5.4L equipped pickup, car or SUV, well...

Bank 1 is the engine bank that holds the spark plugs for cylinders 1, 2, 3, and 4. This bank is the one on the passenger side of the engine (see the illustration in the image viewer).

Bank 2 is the one having the issue. bank 2 is the engine bank that holds the spark plugs for cylinders 5, 6, 7, and 8. This bank is the one on the driver side of the engine (see the illustration in the image viewer).

The main sensors responsible for telling the PCM that there's a problem with the Air/Fuel Mixture are the pre catalytic converter oxygen sensors.

Ford Vehicles:

  • Crown Victoria
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • E150, E250, E350
    • 1997, 1998, 1999, 2000, 2001, 2002
  • Expedition
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009

Ford Vehicles:

  • Explorer (4.6L)
    • 2002, 2003, 2004, 2005
  • F150, F250
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
  • Mustang (GT & Cobra)
    • 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Ford Vehicles:

  • Thunderbird
    • 1995, 1996, 1997

Lincoln Vehicles:

  • Aviator
    • 2003, 2004, 2005
  • Mark VIII
    • 1995, 1996, 1997, 1998

Lincoln Vehicles:

  • Navigator
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
  • Town Car
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Mercury Vehicles:

  • Cougar
    • 1995, 1996, 1997
  • Grand Marquis
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Mountaineer (4.6L)
    • 2002, 2003, 2004, 2005

“I bought a perfect second car... a tow truck.”
Rodney Dangerfield

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