DTC P0171 – How To Find Intake Leaks

DTC P0171 – How To Find Intake Leaks


One of the most frustrating check engine light OBDII codes in existence are codes like DTC P0171 for System Lean Condition. What this means is that something in your vehicle is causing the engine to run lean, or without the proper amount of fuel. Because so many sensors and factors go into this very complex equation, customers can have problems diagnosing this code.

Many times people simply replace sensors without doing the investigation. We can’t count how many times customers take the OBDII error code at face value, and simply replace very expensive parts. Parts like the mass air flow sensor (MAF) or replace fuel pressure regulator (FPR), only to have the code return.


This vehicle has both P0171 and P0174 triggered on the Malfunction Indicator Lamp (MIL), which is a tell tale sign that there’s a larger problem at hand. Because both banks of the Ford V6 engine are running lean, chances are that the MAF or fuel pressure is the culprit.

For a good example of misunderstanding OBDII trouble codes, or misdiagnosing them we’ll be addressing a P0171 OBDII check engine code in a 2006 Ford F-150 with the 4.2 liter V6 with a VIN ID of 2. This customer’s truck is basically stock, and was diagnosed with a P0171 DTC. Upon replacing the MAF sensor, the customer was dismayed to discover that the trouble code did not disappear.



Because the OBDII DTC P0171 is for a Lean condition in your engine, and the MAF is the primary sensory input for your Ford ECU, something as small as intake leaks can cause you major headaches. This is what our how to find intake leaks DIY guide to repairing the OBDII P0171 error code is for.

Today we’ll be showing you how to diagnose the P0171 trouble code, and find intake leaks which can contribute to the P0171 trouble code. The MAF we’ll be working on is part number 3L3Z-12B579-BA, and it can also be found under 3W4Z-12B579-AB.

The things to check when you have a P0171 error code


  • Check Fuel Pressure
  • Check MAF Operation
  • Check Battery Voltage

Because all these things checked out with this customer’s truck, we’ll be checking the system for any intake leaks using a small spray bottle filled with soapy water. To learn how to find intake leaks, start your engine and make sure to stay clear of your cooling fans or serpentine drive belts. Gently spray the solution over the intake pipe and tract and look for any bubbles.


It doesn’t take long for us to find that this intake system on the 2005 Ford F-150 is woefully designed. Large cumbersome plastic tanks make up the MAF housing, and the way in which they seal the MAF just isn’t very conducive to leak free operation. We’ll be taking the intake pipe and MAF housing apart on this Ford truck, in order to tape the connections for a tighter fit.

Begin our how to find intake leaks DIY guide, disconnect the negative terminal on your battery to prevent any accidents. Unclamp one half of the MAF housing and intake tract by loosening the huge accordion clamp shown above.


Once you have this clamp loosened, go ahead and undo the worm clamps that hold the intake tract to the truck’s MAF housing. Your Ford MAF is located on the underside of this MAF housing, and covered by a weatherproof plug.


When you remove this clamp, your MAF housing can come off the intake pipe to your F-150. Remove the entire MAF housing and rotate to expose the underbelly and the large MAF plug.


This plug is the only one that you won’t be re-sealing with tape or weather stripping. Because this plug is after the MAF, there’s no chance of unmetered air to enter your engine.


Reach into the opening with a flat head screwdriver and pull the red release pin to your MAF connector. Now depress the plastic MAF connector and unplug the unit. Your Ford F-150 MAF housing should now be free of your engine bay. Remove the entire MAF housing, and using your flathead screwdriver, pop out the inner MAF tube.


Here’s the part of our how to find intake leaks guide where you can either choose to remove and replace the MAF sensor. The part numbers for this Ford MAF are shown above, if you are in hurry and need this part, we have a few cutover part numbers for this mass air flow sensor.

  • 1F7013210
  • 1F7013210A
  • 4G7Z-12B579-AB
  • 6L3Z-12B579-A
  • L3H513215

These part numbers cutover to Lincoln and Mazda MAF sensors, and can be used for your F-150. Make sure to check your VIN code for interchage parts, as always in our Pro Street DIY Guides.


Now you’ve got to remove the rest of your intake pipe. Disconnect the worm clamps leading to your throttle body, and then you’ve got the PCV connector left.


This connector comes loose after you pull on the green pull tab. Once this green pull tab has been released, you can gently pry off the PCV hose.

Now that you have your full intake disassembled, go ahead and seal up the leaks in question. Tape over the throttle body mounting points, do not cover or block the throttle body. When you re-install your intake piping, make sure that it’s as tight a fit as possible.

Remember that you are eliminating intake leaks, so make sure to that each one of the coupling connections is taped before you slide the intake back on. Every single connection should be resealed or modified so that there’s a greater seal or less chance of air entering the engine unmetered by your Ford MAF.

Have any questions about OBDII DTC P0171 or P0174? How to find intake leaks? how to fix or test your MAF? or replace your fuel pressure regulator? Check out more guides from Pro Street below.

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