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2001 Ford Ranger reading 2 different emission codes

Tiny
MACKISUS
  • MEMBER
  • 2001 FORD RANGER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 66,500 MILES
Check engine light comes on. The code was PO175 -- too rich. Replaced one of two oxygen sensors, downstream from cat converter. Reset, now the error code reads the opposite, PO171, too lean. Only problem noticed is at startup it kind of acts like it's choking to keep running. Other than that seems to run OK. Replace other sensor, upstream from cat convertor? Perplexed. Thanks!
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Wednesday, March 24th, 2010 AT 2:33 PM

15 Replies

Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Ok if you would get some mass air flow cleaner and clean the mass air flow unit. Don't use any other cleaner only mass air flow cleaner. Then clear the codes and see if it comes back and we will go from there.
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Thursday, March 25th, 2010 AT 9:02 AM
Tiny
MACKISUS
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Roger that. I work for Carquest and asked the counter guy about a MAF problem. He said you cannot take those apart. They have the tamperproof screws. Can you clean one without taking it apart?

I will purchase some today when I go in.
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Thursday, March 25th, 2010 AT 12:38 PM
Tiny
RACEFAN966
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Yes you can take it apart I had to on my Mustang to put in a cold air intake system there are no tamper proof screws. Yes you can clean it without taking it apart too but you do need to remove it from the truck. When you buy one you don't get all plastic you only get the sensor see pic below. Also the pic below shows you the hole in the sensor that is what is really needing to be cleaned. Let me know how it goes.


https://www.2carpros.com/forum/automotive_pictures/249564_mass_1.jpg

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Friday, March 26th, 2010 AT 10:13 AM
Tiny
MACKISUS
  • MEMBER
  • 8 POSTS
OK racefan I sprayed the wires see pic. Reset code at neg bat terminal. The CEL usually comes on after 3 days of driving. Wait and see. Thanks.


https://www.2carpros.com/forum/automotive_pictures/506220_MAF001_7.jpg

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Friday, March 26th, 2010 AT 4:19 PM
Tiny
RACEFAN966
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Ok great the only thing is the battery cable removal don't reset the light. It may turn it off but the code is still there. So what you really need to do is hook up a scan tool and clear it. Let me know if it comes back on and what code comes up if it does.
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Monday, March 29th, 2010 AT 9:20 AM
Tiny
MACKISUS
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Yes, you were exactly right. The CEL did come on this very evening. I cleared it with a scanner and there were two codes; PO171 and PO174. PO174 is one that has never shown up before. The last two were PO175 and PO171, respectively. I will drive it and wait to see what happens next?
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Tuesday, March 30th, 2010 AT 5:35 AM
Tiny
RACEFAN966
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Ok that work. Now if it does come on again with the same codes then what I will need you to do is ohm the coolant temp sensor and do this when the truck is cold. Get the ohms and the temp at the time you checked it. Thanks.
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Tuesday, March 30th, 2010 AT 9:31 AM
Tiny
MACKISUS
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I have an ohmeter but do I need to take it out of the truck to test it? My chilton shows it on the front lower part of the intake. ALSO I notice me reservoir is low; no water at the cold level.
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Thursday, April 1st, 2010 AT 2:55 PM
Tiny
RACEFAN966
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No you do not remove it you simply unplug it ohm it (do this when the truck is cold) and then get back to me with the ohms and air temp at the time.
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Friday, April 2nd, 2010 AT 9:56 AM
Tiny
MACKISUS
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I can't get to the sensor w/o much difficulty. Would it be the one that's gray or red? When you say to "ohm" it, I think you mean to take off the connector and take a resistance check between the two terminal ends right?


https://www.2carpros.com/forum/automotive_pictures/506220_sensors_2.jpg

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Friday, April 2nd, 2010 AT 12:57 PM
Tiny
RACEFAN966
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Ok this sensor should be next to or very close to the thermostat housing. Yes just unplug it and check resistance between terminal ends on the sensor not the wiring harness. Check pics below it also depends on the engine it may look different. Don't know if yours is 3.0 or 4.0 V6.


https://www.2carpros.com/forum/automotive_pictures/249564_276517_1.jpg

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Saturday, April 3rd, 2010 AT 9:39 AM
Tiny
MACKISUS
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Mine is a 4.0L V6. I read in another blog that you must remove the intake to get the clips off of the coolant sensor. Do you agree? I replaced the plugs, wires, air filter; but I also found this gash in a vacuum line to the intake. Could this be the culprit?


https://www.2carpros.com/forum/automotive_pictures/506220_gash_in_hose_2.jpg

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Saturday, April 3rd, 2010 AT 10:56 PM
Tiny
RACEFAN966
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Ok if this vacuum line has a hole in it and is leaking vacuum then yes this could cause a problem. Fix it and see if it inproves. Let me know how it goes.
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Tuesday, April 6th, 2010 AT 9:46 AM
Tiny
MACKISUS
  • MEMBER
  • 8 POSTS
Been about a week now, no CEL. It was either the gash in the hose to the intake, or replacing the spark plugs. I noticed the [taken out] plugs were gapped really wide. But with good color and no sign of fouling. Probably never changed before. And with over 66K miles. Thanks for your help racefan.
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Saturday, April 10th, 2010 AT 12:05 AM
Tiny
RACEFAN966
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Great sounds like you found the problem either way. You did gap the plugs as recomended on the under hood sticker? Anyway great job and have a great weekend.
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Saturday, April 10th, 2010 AT 7:47 AM

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