Code help
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Senior User
Joined: Dec 2001
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From: MN
Code help
I know there is a lot of info concerning the P0171 code on the forum but most of them are either a different engine than mine or in combination with other codes or conditions. That being said, my check engine light came on two days ago and stays on constantly. I took it to autozone and they said the code was P0171. My Haynes manual says "System adaptive fuel to lean (Bank 1). So, first of all which side is bank 1, is it driver's side or passenger side? I understand from reading the forum that this could be oxygen sensors, intake leaks and/or vacuum leaks. If it was oxygen sensors would it be the one before the cat or after or both? Where is the best place to start? Engine runs fine, no stumbles or hard starting and gas mileage is not great but hasn't changed. Thanks for the help. This is for a 2000 Ranger with 4.0L OHV 5-speed 4wd.
Post Fiend
Joined: Jan 2003
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From: Connecticut
Bank 1 = Passenger Side.
"Upstream" (before the cat) 02 sensors are the ones that help manage fuel control and ones you care about if you have lean codes.
"Downstream" (after the cat) 02 sensors have nothing to do with fuel control, they don't do anything except tell the PCM that the cats are still working.
Regarding vacuum leaks, you might consider the upper intake o-ring gaskets, as well.
"Upstream" (before the cat) 02 sensors are the ones that help manage fuel control and ones you care about if you have lean codes.
"Downstream" (after the cat) 02 sensors have nothing to do with fuel control, they don't do anything except tell the PCM that the cats are still working.
Regarding vacuum leaks, you might consider the upper intake o-ring gaskets, as well.
Senior User
Joined: Feb 2005
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depending on mileage might want to remove and clean oxygen sensors, and check for vacuum leak. Plastic vacuum lines get brittle and break easily, or get knocked off when doing other repairs and go unnoticed.
www.mobilefleetservices.net
www.mobilefleetservices.net
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From: MN
Thanks for the responses. I've read that a lot of times once the engine heats up, the upper intake gasket leaks disappear cause they expanded with the heat. My check engine light hasn't gone out since it came on so I'm gonna leave that to the last resort. I'll do a visual inspection of vacuum hoses and then maybe replace the oxygen sensors. They probably need replacing anyway.
Former ******
Joined: Nov 2004
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From: Salt Lake City, Utah
Yeah, O2 sensors really should be replaced every 80,000 miles as preventative maintenance. They really can't be cleaned. The code doesn't really say you have a bad O2, so I would look for leaks first. Exhaust leaks can cause lean codes, so don't rule out an exhaust leak as a possible culprit.
Post Fiend
Joined: Oct 2005
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From: Kiev, Ukraine
I have this code periodically appearing. I clear codes and later this code appeares againe. I suggest that I have cracked air intake (truck was rolled over, had to replace bent hood and grill). So I think I need a manual how to remove and install air intake of 4.0 SOHC.
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From: MN
Ok, I've done a visual inspection and didn't find any hoses off or visibly cracked or anything. I didn't hear any hissing over the sound of the engine or out of the ordinary. There are a million vacuum hoses some of which have the black plastic protectors over them. Not sure how a person is supposed to check all of them. Any suggestions? My check engine light has not gone off since it came on. I know when I've had a bad O2 sensor in my 1990 5.0L, the light would go on and off intermittently. Maybe the newer vehicles are different. I have not done any work on my truck lately so I know I didn't knock a hose off or anything. This is really frustrating.
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Post Fiend
Joined: Jan 2003
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From: Connecticut
You can try cleaning the MAF: https://www.ford-trucks.com/forums/1...-cleaning.html
The odds of both 02 sensors going bad at exatly the same time are negligible. So if it's not a dirty MAF, then it's gotta be a vacuum leak somewhere. Maybe doing a propane sniff test around all the hoses and upper intake area will find something.
The odds of both 02 sensors going bad at exatly the same time are negligible. So if it's not a dirty MAF, then it's gotta be a vacuum leak somewhere. Maybe doing a propane sniff test around all the hoses and upper intake area will find something.
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From: MN
Today I cleaned the MAF and disconnected the battery for about an hour. The alarm scared the crap out of me when I reconnected the battery, lol. The check engine light has not come back on. We'll see how long it lasts. The autozone info about the code P0171 says that it could be the MAF but would usually require the code for bank 2 being lean as well, which mine did not have. So, I'm not real confident that cleaning the MAF is what made the code go away. I think just resetting by disconnecting the battery cleared the code out and it hasn't come back on yet. We'll see.