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P0172 Banks One and Two - MAF Cleaning 201

12/23/2004, UD 02/27/2005

I had a check engine light come on today and went to AutoZone to get it read. The code is P0172 banks one and two. The code was in the car twice. I looked up on V8 SHO to try to find a way to fix it and I got confused with all the info. What is really wrong with my car? I do have the symptoms of a MAF contamination. Lack of power, buck/jerks, hesitation/surges on acceleration. How do I go about cleaning or getting this problem fixed without spending too much money? Please help with this.

Another question. What would be another gauge to have? I have an oil pressure one and room for one more. Trans temp, pressure, water, or volts? This will help with my custom gauge holder.

Rob Ziehm
97 ES
The code is for Lean Adaptive Limits Reached. These are not oxygen sensor codes, they are an indicator that the engine is simply running too lean. As the engine runs, the computer adjusts the fuel trims to compensate and "hunt" stoichiometry. It never attains it, but it does shoot for it. A perfect running engine will have fuel trims that bounce around -0-. Sometimes (-), sometimes (+) and bouncing back and forth. When the engine is running too lean, it'll have positive fuel trims. Then computer is trying to fatten up the mixture. If the engine is too rich, the computer will try and lean out the mixture by pulling fuel out with a negative number. If you have the same code for both banks, the problem is common to both sides of the engine. The first place I'd look is the MAF sensor. This sensor is the main source of info for the computer to calculate "load". Then "load" is used for fuel delivery. The O2 Sensors are there as feed back and for the computer to make adjustments to the fuel delivery, these are called fuel trims. If the engine is running too rich or too lean, the fuel trims can compensate, but only to a point. When they reach their limits, the computer kicks on the light and it's off to AutoZone to pull the codes.

So, my advice is to start by looking at the MAF wires. If you are running a K&N filter or other tack oil based air filter, the oil from the filter can migrate to the wires of the MAF. This tack oil attracts dust and other particulates that do get past the filter and they build up on the wires of the sensor. This buildup disturbs the air flowing over the sensor wires and gives the computer incorrect information. This causes the engine to run poorly and the O2 sensors report this back to the computer. The problem could also be a vacuum leak, but whatever the problem, it's common to the whole engine. It could be a fuel pressure problem too, but that's much less likely.

Clean the MAF first and report back.
Doug Lewis
Ford Performance Specialists Inc.
Atlanta Georgia (770) 949-7191
What is the proper way to clean the MAF? Would a spray on electronics cleaner be acceptable or maybe a can of compressed air like you would use to clean your keyboard?
Jason Barker
Yeah, remove the two T-20 Torx head screws and pull the sensor out of the meter. I use carb cleaner and then brake parts cleaner to remove the carb cleaner residue. Then blow it off with a little compressed air until dry and reinstall.

Doug Lewis
Ford Performance Specialists Inc.
Atlanta Georgia (770) 949-7191
Or just use quick-drying electronic contact cleaner. Make sure the package says "leaves no residue". I use a product called "Lectra-motive" which has more of a high-pressure liquid jet effect than a loose aerosol spray pattern. It also happens to be cheaper. :-)

I give the MAF a good cleaning about every 10K miles or so.

See Also:MAF Cleaning

Uncl Lar


Hey folks looking for some insight on the recurring P0172 Bank 1 too rich condition. The car feels like it should have a little more oomph. I have some concerns about tracking this one down however because the previous owner had the cats and resonator removed for 'better' exhaust sound along with replaceing the oem intake with a K&N cone in the engine bay. I am wondering if the second O2 sensor on bank 1 (diagram shows it located after the cat) is triggering this, maybe a contaminated MAF, or what else causes this condition? Vacuum leak? Faulty injector? Any input appreciated.


Possible causes:

Fuel system

Excessive fuel pressure.
Leaking fuel injector(s).
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Contaminated fuel injector(s).
Vapor management valve (VMV) leaking.
Induction system

Air leaks after the MAF.
Vacuum leaks (vacuum lines and gaskets).
Restricted air inlet.
PCV system.
Fuel purge system.
Improperly seated engine oil dipstick.
EGR System

leaking gasket.
Stuck open EGR valve.
Leaking diaphragm.
Base engine

Oil overfill.
Cam timing.
Cylinder compression.
Exhaust leaks before or near the HO2S(s).
Check intake air system for leaks, obstructions and damage.
Check air cleaner element, air cleaner housing for blockage.
Verify integrity of the PCV system.
Check for vacuum leaks.

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