Ford Escort ZX2 2001 throwing code P0171 Adaptive Fuel Trim Too Lean (Bank 1)


Asked by Jan 02, 2016 at 04:38 PM about the 2001 Ford Escort 2 Dr ZX2 Coupe

Question type: Maintenance & Repair

P0171 Adaptive Fuel Trim Too Lean (Bank 1)

Any ideas?

From what I've read up on there's the possibility that the error could be the result of the mass air
flow sensor being too dirty. I'm not sure of how to clean it.

Most tutorials for cleaning air flow sensors indicate that there are screws that need to be undone,
but there are no screws on this. It looks like the one in this video:

It looks like it's just a plug.

The guy there says it's possible to spray the cleaner in there but I don't want to just start spraying
stuff inside with no guarantee that I'm actually getting at the sensor.

What can I do? Is there any way to get the sensor out?

7 Answers -see that page. Likely the PCV valve. The article talks about 02 sensors, but does NOT mean the sensor is bad. It is only doing what it's suppose to do, send data to PCM

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Best Answer Mark helpful

Thanks. I'm looking up more information on the PCV valves now. What makes it most likely that that is causing the problem? I'm not familiar with fixing cars. Do you think this would be expensive to take to a mechanic?

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They are not screws, they are big hose clamps that you can use a screwdriver or a 5/16 or1/4 socket

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It could be expensive, but only because mechanics are expense. a PCV valve cost about $5 and takes 10 minutes to replace. The reasson I say PCV is one cause of lean running is a vacuum leak, and the PCV draws more vacuum than any other thing on an engine. But the vacuum leak could be anywhere, I'm not sire if this car has a vacuum brake booster, but that is a big vacuum hose also. And any of the small vacuum lines loose, dangling, or any nipples with nothing attached, look for that

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Just to elaborate, a vacuum leak is unmetered air getting in to intake, the MAF being the meter. Then the PCM adjusts the fuel/air but overcompensates because it relies on the MAF to 'tell' it how much air is flowing

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Thanks for your help so far. I'm going to check out the PCV valve tomorrow since it's too dark out now to do anything. Here's hoping this will wind up an easy fix.

1 people found this helpful.

Okay, so upon checking out the car this morning, I realize I have no idea what I'm looking at. Not sure if none of the images I've seen of it so far match up exactly, or if there's just so much stuff in the way that it's causing me to confuse what's what. Would you be able to identify the PCV valve/tube in this photo?

Your Answer:


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