The infamous P0171
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Junior User
Joined: Oct 2001
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The infamous P0171
Has anyone had any experience with an intermittent P0171 fault code?
I have a ’97 4.0 AWD and the darned check engine light pops on every other week or so.
It only seems to happen when the van is going through the warm up cycle on the first trip of the day. If you I reset the computer the light stays off for a week or two and then ‘hello” the old friend pays a visit.
I have cleaned the airflow sensor, put in a new O2 sensor, checked for vacuum leaks and pretty well followed the whole symptom check list that ford says to follow. If the darned light would come on every time I might be able to find the fault.
How about the coolant temp sensor? Could it cause a lean fault code?
I have a ’97 4.0 AWD and the darned check engine light pops on every other week or so.
It only seems to happen when the van is going through the warm up cycle on the first trip of the day. If you I reset the computer the light stays off for a week or two and then ‘hello” the old friend pays a visit.
I have cleaned the airflow sensor, put in a new O2 sensor, checked for vacuum leaks and pretty well followed the whole symptom check list that ford says to follow. If the darned light would come on every time I might be able to find the fault.
How about the coolant temp sensor? Could it cause a lean fault code?
Freshman User
Joined: Sep 2003
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I have a 97 4.0 AWD also and am getting the same code. My research points to the mass air flow sensor-after talking with a Ford engineer and reading the documents on the Air Flow sensor it seems that cleaning may not be sufficient and replacement of the sensor may be required.Before running out to the auto parts store the Ford engineer warned me that on the OBD-II systems that codes may be transmitted that may not neccessarily effect driveability.This he said is due in part to the stringent emissions requirements that Ford was required to meet. Basically if its not impacting performance I wouldnt be too concerned-the Air Flow sensor is around $100 so weigh the costs versus the return on investment.
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Junior User
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More on P0171
I have been told that another problem can be the use of a K&N air filter. Something about the oil used on the filter contaminating the MAS. I hope this isn't true as I like K&N filters. The light hasn't been on for a while now, but I am sure it will be back.
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Joined: Sep 2003
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I just replaced the MAF on my 97 4.0 and it got rid of the infamous P0171 code for good. Rather than lay out big bucks to Ford I went to my local junkyard and they dug one out of their storeroom from a 4.0 Explorer -$20 and it runs like new again. I had cleaned the old MAF three times and it still gave the P0171. Just check the last two letters on your MAF either CA or DA and you can get one from an Explorer or Aerostar and probably several other cars. The Explorer sensor was very clean as their application had the sensor sealed inside a big air drum.When the drum was opened the sensor looked as new and more importantly worked like new.
